# 50 cal (high rate of fire) vs 20mm cannon (hitting power)



## grampi (Oct 29, 2020)

If you were a fighter pilot in WWII, would you rather have the high rate of fire of the 50 cal, or the hitting power of the 20mm? I personally feel the 50 cal was plenty hard hitting enough to take out ANY aircraft, and its high rate of fire made it even more effective...the slow rate of fire for the 20mm meant you had to be a much better marksman...


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## tomo pauk (Oct 29, 2020)

grampi said:


> If you were a fighter pilot in WWII, would you rather have the high rate of fire of the 50 cal, or the hitting power of the 20mm? I personally feel the 50 cal was plenty hard hitting enough to take out ANY aircraft, and its high rate of fire made it even more effective...the slow rate of fire for the 20mm meant you had to be a much better marksman...



The Italian .50 was good for 700 rd/min (down to 550 rd/min when synchronised). Shvak was a bit faster, up to 800 rd/min un-synchronised. Muzzle velocity was about the same. HE shell for the Breda .50 was 34g, for Shvak was 96 g heavy.

20 mm FTW.


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## Clayton Magnet (Oct 29, 2020)

The 20mm Hispano and Browning M2 had similar rates of fire, and similar muzzle velocities.


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## swampyankee (Oct 29, 2020)

The USN rated the 20mm as three times as effective as the 0.5 in, at least when it worked. I’ll take a working Hispano.


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## Shortround6 (Oct 29, 2020)

AS Tomo and CM have pointed out the rates of fire for both calibers of gun varied quite a bit.

For an american pilot the difference in rate of fire was 600rpm for the 20mm and 800rpm for a wing mounted .50cal (give or take) so the difference in rate of fire was not that different per gun. A four cannon Corsair was firing 40 20mm shells per second, a six .50 cal Corsair was firing 78 or so .50 cal bullets per second. The 20mm shells had about the same muzzle velocity and weighed almost 3 times as much, and they exploded (mostly)  

Most service 20mm cannon fired at least 500rpm (early German and Japanese guns) while later German (MG 151) and Japanese army (Ho-5 cannon) fired at 700-750 rounds a minute. U.S. .50 cal fired 1 to 2 bullets more per second. or about 13% more at best. The Axis 20mms hit harder per projectile. 

We have a lot of threads on the subject.

The U.S. 50 did the job but it was no wonder weapon.

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## pbehn (Oct 29, 2020)

If you are chasing a V1 "cruise missile" in 1944 a cannon is the thing to have.


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## gottschs (Oct 29, 2020)

Folks, my opinion depends on whether you are taking on a 4-engine bomber or a light/medium bomber/fighter. I want more lead heading down range to hit a Japanese or German fighter since they are maneuverable while I would want a 20mm for taking on a heavy bomber because it takes a lot less of them to bring down a heavy bomber (plus they can have an explosive round). The USAAF and USN were very lucky that they were taking on flammable IJN/IJAAF aircraft and German fighters with their .50 cal (same goes for the RAF using 6-8 .303 round guns to take on HE-111/JU-88/DO-17's). Just my opinion.


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## PAT303 (Oct 29, 2020)

Unless I'm chasing A6M's I'll have a MkXIV fitted with two Hispano's loaded with 300 rounds of SAPI's each and 280g of fuel, and let me at 'em.


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## pbehn (Oct 29, 2020)

As has been said there are many threads on this. In 1939 the RAF armament was 8 x 303 MGs and that was considered devastating, enough for a 2 second burst to take down a bomber, the effectiveness was increased with incendiary rounds. However even then the preferred armament for a fighter was for 4 x 20mm cannon, that's what the Whirlwind was all about. Prior to the USA entering the war the RAF standard armament for fighters was 4 x 20mm cannon. This was fitted to the Hurricane Mk2, the Typhoon Tempest Mosquito and Beaufighter. The Spitfire was an exception, they started to fit cannon in 1940, and had problems getting them to work, but even when it did work the decision was to have 2 cannon and 4 x 0,303mgs for various reasons, weight at high altitude and heating. While RAF pilots may have preferred cannon in the BoB, it is a fact that the LW ran out of serviceable bombers and gave up. But the Spitfire wasn't limited to 2 cannon and 4mgs by any law, some carried 4 cannon and 4 x 0.303 mgs which would ruin anyone's day.

There are statistics already discussed about rate of fire, you can then discuss weight of fire and effect of fire but the LW had another statistic of how many hits you could land in a "pass" and how effective those hits would be. This is concerned with bringing down a 4 engine bomber, but the problem then becomes the ballistics of large calibre rounds even rockets that can devastate a large bomber become increasingly unlikely to hit a fighter.

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## Koopernic (Oct 29, 2020)

pbehn said:


> As has been said there are many threads on this. In 1939 the RAF armament was 8 x 303 MGs and that was considered devastating, enough for a 2 second burst to take down a bomber, the effectiveness was increased with incendiary rounds. However even then the preferred armament for a fighter was for 4 x 20mm cannon, that's what the Whirlwind was all about. Prior to the USA entering the war the RAF standard armament for fighters was 4 x 20mm cannon. This was fitted to the Hurricane Mk2, the Typhoon Tempest Mosquito and Beaufighter. The Spitfire was an exception, they started to fit cannon in 1940, and had problems getting them to work, but even when it did work the decision was to have 2 cannon and 4 x 0,303mgs for various reasons, weight at high altitude and heating. While RAF pilots may have preferred cannon in the BoB, it is a fact that the LW ran out of serviceable bombers and gave up. But the Spitfire wasn't limited to 2 cannon and 4mgs by any law, some carried 4 cannon and 4 x 0.303 mgs which would ruin anyone's day.
> 
> There are statistics already discussed about rate of fire, you can then discuss weight of fire and effect of fire but the LW had another statistic of how many hits you could land in a "pass" and how effective those hits would be. This is concerned with bringing down a 4 engine bomber, but the problem then becomes the ballistics of large calibre rounds even rockets that can devastate a large bomber become increasingly unlikely to hit a fighter.



Some carried 2 x 20mm and 2 x 0.5 on the universal wing. They could be fitted with 4 x 20mm but this created handling issues. The 20 series Spitfires which had a new wing and cut of hispanos seemed to work fine.


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## pbehn (Oct 29, 2020)

Koopernic said:


> Some carried 2 x 20mm and 2 x 0.5 on the universal wing. They could be fitted with 4 x 20mm but this created handling issues. The 20 series Spitfires which had a new wing and cut of hispanos seemed to work fine.


It was discussed on the forum here, some Spitfire MkVc had 4 cannon and 4 mgs, used in the Med theatre, I was surprised to read it too.

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## fastmongrel (Oct 30, 2020)

If your engine is hit by a couple of .50 armour piercing incendiaries they might hit an oil line or a fuel line. If your engine is hit by one 20mm HE round that explodes you have lots of hot shrapnel spraying all over the engine compartment like shotgun pellets. Two.50 rounds is two hits one 20mm round is lots of hits.


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## fastmongrel (Oct 30, 2020)

pbehn said:


> It was discussed on the forum here, some Spitfire MkVc had 4 cannon and 4 mgs, used in the Med theatre, I was surprised to read it too.



There's a picture of a Spitfire with 6 cannon. Don't know if they were dummies maybe for aerodynamic testing but imagine being hit by 6 20mm HE rounds. That's one burst B29 killing power.


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## gottschs (Oct 30, 2020)

pbehn said:


> As has been said there are many threads on this. In 1939 the RAF armament was 8 x 303 MGs and that was considered devastating, enough for a 2 second burst to take down a bomber, the effectiveness was increased with incendiary rounds.



Recommend reading this article about a P-61 with 20mm and .50 cal's trying to take down a B-29 https://www.flightjournal.com/wp-content/uploads/2011/12/splash1.pdf

8 x 303's aren't going to take down a B-17 or B-29 very easily while I agree completely 8 x 303's will do great against a LW DO-17/JU-88/HE-111.

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## pbehn (Oct 30, 2020)

fastmongrel said:


> There's a picture of a Spitfire with 6 cannon. Don't know if they were dummies maybe for aerodynamic testing but imagine being hit by 6 20mm HE rounds. That's one burst B29 killing power.





fastmongrel said:


> If your engine is hit by a couple of .50 armour piercing incendiaries they might hit an oil line or a fuel line. If your engine is hit by one 20mm HE round that explodes you have lots of hot shrapnel spraying all over the engine compartment like shotgun pellets. Two.50 rounds is two hits one 20mm round is lots of hits.


The standard armament of a Mosquito or Beaufighter would ruin anyones day. 4 x 20 mm firing at 600 (as a round number) RPM means a 2 second burst is 80 shells, it wouldn't only wreck an aircraft but made a mess of shipping too, it wouldn't sink a ship but damage much of the superstructure. The same could be said of a P-47s 8 x 0.5 mgs. Two seconds of those would wreck any aircraft made. One thing I noticed from reading pilots memoirs, it didn't seem to matter where a Hurricane or Spitfire was hit by a cannon shell, if it wasn't in the engine, wing tips or tail the pilot frequently got injured in some way by splinters, usually in the legs.


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## fastmongrel (Oct 30, 2020)

pbehn said:


> 4 x 20 mm firing at 600 (as a round number) RPM



I have seen various rates of fire from 600 to 700 for the Hispano MkII so I usually write 650 rpm not that it makes a great deal of difference it will just make you 10% deader. The later Hispano MkV was 750 rpm.


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## pbehn (Oct 30, 2020)

fastmongrel said:


> I have seen various rates of fire from 600 to 700 for the Hispano MkII so I usually write 650 rpm not that it makes a great deal of difference it will just make you 10% deader. The later Hispano MkV was 750 rpm.


As I said it is a round and not unreal number (600 is 10 per second), the advised firing time for pilots was 2 seconds, no reason at all why it couldn't be longer.


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## PAT303 (Oct 31, 2020)

pbehn said:


> One thing I noticed from reading pilots memoirs, it didn't seem to matter where a Hurricane or Spitfire was hit by a cannon shell, if it wasn't in the engine, wing tips or tail the pilot frequently got injured in some way by splinters, usually in the legs.



From what I have read it didn't matter what plane your were in, if the rounds entered off bore they bypassed the rear armor and pilots got arm and leg injuries.


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## A.G. Williams (Nov 1, 2020)

Here's a detailed analysis of the effectiveness of different kinds of WW2 fighter armament: WORLD WAR 2 FIGHTER GUN EFFECTIVENESS

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## wuzak (Nov 1, 2020)

fastmongrel said:


> There's a picture of a Spitfire with 6 cannon. Don't know if they were dummies maybe for aerodynamic testing but imagine being hit by 6 20mm HE rounds. That's one burst B29 killing power.



It was a mockup on the prototype Mk IV/XX/XII Griffon Spitfire.


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## jmcalli2 (Nov 5, 2020)

grampi said:


> If you were a fighter pilot in WWII, would you rather have the high rate of fire of the 50 cal, or the hitting power of the 20mm? I personally feel the 50 cal was plenty hard hitting enough to take out ANY aircraft, and its high rate of fire made it even more effective...the slow rate of fire for the 20mm meant you had to be a much better marksman...



The question has to go beyond the rate of fire and size of the shell. You have other important considerations, such as:
Reliability - Shoot, it won't shoot!
Production/parts availability
Ammunition capacity; how many seconds of shooting do you need?
What is you intended target, bomber, fighter, tank?

20mm ammo may be more effective than .50 cal, but how many rounds can you carry? 
Take a P-51; ~300 rounds/gun for .50 cals, 60-120 rounds/gun for the 20mm. It's size and weight that limit the 20mm ammo.

Here's an interesting reference site:

The WWII Fighter Gun Debate: Gun Tables

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## fastmongrel (Nov 5, 2020)

jmcalli2 said:


> 20mm ammo may be more effective than .50 cal, but how many rounds can you carry?
> Take a P-51; ~300 rounds/gun for .50 cals, 60-120 rounds/gun for the 20mm. It's size and weight that limit the 20mm ammo.
> 
> Here's an interesting reference site:
> ...



P51 should have been able to carry more than 120 rounds per gun. The wing had similar volume to a Tempest which carried 200 rounds per gun.


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## Vic Nighthorse (Nov 5, 2020)

I imagine that this has also been covered many times before but were more air to air fighter kills from attacks on unaware targets or against evasively maneuvering targets? If your target is unaware a lower velocity and lower cyclic rate wouldn't be as big of disadvantages but mineshell like damage would still be as much of an advantage as ever, no? These are sincere rather than rhetorical questions.

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## jmcalli2 (Nov 5, 2020)

fastmongrel said:


> P51 should have been able to carry more than 120 rounds per gun. The wing had similar volume to a Tempest which carried 200 rounds per gun.


The US 20mm Hispano round is ~1/2 inch longer than the .50cal Browning round and is ~ 3 x as heavy. The P-51D carried 1840 rounds of .50cal. That would limit the P-51 to ~600 total rounds for four 20mm by weight, about 150 rounds/gun.
The Tempest wing was thicker than the Mustang, so it's not surprising it would carry more ammo.

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## jmcalli2 (Nov 5, 2020)

fastmongrel said:


> P51 should have been able to carry more than 120 rounds per gun. The wing had similar volume to a Tempest which carried 200 rounds per gun.


The P-51 wing area was 235 sq ft, the Tempest was 302 sq ft. The Tempest wing was also thicker. The Tempest was a a much larger aircraft, weighing ~50% more empty than a P-51, ~11,400 lbs to ~7,600 lbs.


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## Shortround6 (Nov 5, 2020)

The P-51s with cannon could carry up to 125rpg. They came after the drums, no 60 round capacity problem. Weight shouldn't have been a big issue as the ones with cannon didn't carry bombs or drop tanks so there is nothing to trade off. 

The A-36 and P-51A carried two .50s in each wing and carried 250rpg for the inner guns and 350rpg for the outer guns. As did P-51Bs & Cs.

What a hypothetical version of a P-51D might carry may be a different discussion.

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## Glider (Nov 5, 2020)

jmcalli2 said:


> The 20mm Hispano is ~1/2 inch longer than the .50cal Browning and is ~ 3 x as heavy. The P-51D carried 1840 rounds of .50cal. That would limit the P-51 to ~600 total rounds for four 20mm by weight, about 150 rounds/gun.
> The Tempest wing was thicker than the Mustang, so it's not surprising it would carry more ammo.



I think it's worth remembering that the Tempest had the Hispano V not the Hispano II.

So 6 x 0.5 M2 weighs more than 4 x 20mm - 174kg vs 168kg
it has an almost identical M/V - 880 m/s vs 840 m/s
it also had a near identical ROF - 800 rpm vs 750 rpm
The 0.5 was shorter 1.65m vs 2.184 meters
plus the 20mm almost certainly had slightly better ballistics

Me, I would take the 4 x 20mm every time.


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## jmcalli2 (Nov 5, 2020)

Shortround6 said:


> The P-51s with cannon could carry up to 125rpg. They came after the drums, no 60 round capacity problem. Weight shouldn't have been a big issue as the ones with cannon didn't carry bombs or drop tanks so there is nothing to trade off.
> 
> The A-36 and P-51A carried two .50s in each wing and carried 250rpg for the inner guns and 350rpg for the outer guns. As did P-51Bs & Cs.
> 
> What a hypothetical version of a P-51D might carry may be a different discussion.



Thanks for the 20mm round capacity info; I couldn't find it and gave up after an hour of looking.

My P-51D was for comparison only, but is weight isn't an issue, why stop at 20mm? Just put 6 37mm into a P-51. 

There was another armament outfit for the P-51, the original one of 2 x .50 cal in the lower nose, 2 x .50 cal in the wings, and 4 x .30 cal in the wings. 

Here's another interesting tidbit: the UAAC combat evaluation of the P-51 made the suggestion the the four 20mm be replaced by four .50 cal. No reason was given, which is sad because I'd love to know what it was - vibration? - reliability? - aim/accuracy? - personal preference? He only references 'standardization' almost as an after thought.
Here's the link to the report:

P-51 Tactical Trials

The armament recommendation is in section 4b of the report.

My understanding is that the British did put four 20mm in a P-51D, but other than a photo (in which the cannon looked pointed about two degrees down. For staffing?) I haven't found much on that either. I blame Glenfiddich.

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## jmcalli2 (Nov 5, 2020)

Glider said:


> I think it's worth remembering that the Tempest had the Hispano V not the Hispano II.
> 
> So 6 x 0.5 M2 weighs more than 4 x 20mm - 174kg vs 168kg
> it has an almost identical M/V - 880 m/s vs 840 m/s
> ...



I think it depends on your mission. The British liked that set up, and the USN moved that way too. The USAAC even went with it in the P-61, and remember many of those did not have the 4 x .50cal turret mounted. In many mission though, more ammo may be what you need at the cost of reduced firepower; escort and interception of dive bombers come to mind.

It's like asking which is a better engine, one that gives you acceleration or one that gives you cruise; are you running the Indy 500 or a 1/4 mile NHRA race?


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## PAT303 (Nov 6, 2020)

Glider said:


> So 6 x 0.5 M2 weighs more than 4 x 20mm - 174kg vs 168kg



The on target effect of twelve brownings in a lighter package than 6, whats not to like about four hispano's.

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## PAT303 (Nov 6, 2020)

jmcalli2 said:


> It's like asking which is a better engine, one that gives you acceleration or one that gives you cruise; are you running the Indy 500 or a 1/4 mile NHRA race?



Four Hispano's are better than 4 or 6 Browning's every way you look at it, each 20mm hit is worth 3 .50 Cals so from single seat fighters to four engine bombers the Hispano's have them covered.


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## BiffF15 (Nov 6, 2020)

Glider said:


> I think it's worth remembering that the Tempest had the Hispano V not the Hispano II.
> 
> So 6 x 0.5 M2 weighs more than 4 x 20mm - 174kg vs 168kg
> it has an almost identical M/V - 880 m/s vs 840 m/s
> ...



I think there is room here for a few more variables. First, if instead of 6 x .50s one went with 4 but increased the ammo it would give a commensurate increase in trigger time. Second, I think in combat there is a “it depends”. Reliability would be number one, or in other words knowing that when I squeezed the trigger that the guns would work. I would take reliability as my number one choice, then increased rounds count (longer trigger time / Mk14 type gunsight?) until I became a confident shooter, then would switch to heavier caliber. 

Food for thought.

Cheers,
Biff

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## jmcalli2 (Nov 6, 2020)

.


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## gottschs (Nov 6, 2020)

I still stand by the key issue is what type of planes are you going up against and the experience of your pilot. If going up against a 4-engine bomber fleet, .303/.50 cal won't do the trick and you need 20 and 30mm. If you going up against a fighter force and twin engine light/medium bombers then I want more ammo and more guns firing (meaning .303 and .50 cal are perfect). Regarding pilot experience, the US had alot of average pilots that had many training hours so I would want them to have plenty of ammo and more guns firing. Stories from experienced Finnish, RAF, and German pilots showed they knew exactly where to hit and used a minimum amount of ammo.

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## pbehn (Nov 6, 2020)

BiffF15 said:


> I think there is room here for a few more variables. First, if instead of 6 x .50s one went with 4 but increased the ammo it would give a commensurate increase in trigger time. Second, I think in combat there is a “it depends”. Reliability would be number one, or in other words knowing that when I squeezed the trigger that the guns would work. *I would take reliability as my number one choice*, then increased rounds count (longer trigger time / Mk14 type gunsight?) until I became a confident shooter, then would switch to heavier caliber.
> 
> Food for thought.
> 
> ...


That was the issue in 1940/41, no one had anything reliable with a high rate of fire. The UK and USA made different choices for different reasons. The discussion today is about the two types after they were sorted and while the cannon may be more effective in a fighter it didn't adapt well to a daylight bombers defence.

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## GrumpyOldCrewChief (Nov 6, 2020)

I don't think I have seen a mention, except in passing, of one of the big reasons the US chose the M2. Production and logistics standardization. Yes, most upper echelon folks knew there were "better" solutions, but also had fears that production or logistics bottlenecks might be leaving fighting outfits with the wrong ammo. Or tools to fix, or whatever else. If everybody uses the same type of item, everybody always gets the right item. As our log tails got better organized, this was less of a real concern, but always remained as a BIG ghost in everybody's thinking. Standardization was viewed by many as a key to large production numbers. As an illustration - was the Sherman a good tank? Maybe, and certainly nowhere near as good, one for one, as many of the German tanks it met. But we could build thousands of them, and keep them in service, because of (relative) standardization. Assurance of meeting the level of performance required, at most times, trumped "best". The M2 performed well enough, often enough, to be the simplest solution. Again, it hadn't the highest RoF, or the highest projectile weight. But, it was the best compromise solution available. 
And don't forget other production issues. If the US wants to use Hisso V cannons in everything, where is that huge number of weapons going to come from? License manufacture is an artform, from initial negotiations, to actual production line problem solving. A whole can of worms that many - right or wrong, better or worse - would not at that time willingly opened.

Most of what we are discussing here was also known to the production planners back then. If my goal is to present the "fightingest" weapons & force available, I would agree, mostly, with them. We get the Monday Morning Quarterback experience. They didn't have that option.

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## A.G. Williams (Nov 6, 2020)

The USAAF - and even more the USN - _were_ interested in cannon as fighter armament; they tested some 23 mm Madsens prewar and wanted to order them, but this was refused on the grounds that the US .9 inch (23 mm) cannon were in development and could do the job. These turned out to be dismal failures (the US did not appear to have any competent gun designers since the death of John Browning) so the US ended up following the UK lead and buying the Hispano. This was a problematic gun, as the UK had discovered, but the US managed to make an even bigger mess of it, and it was never regarded as reliable (see Modifications and Attempts at Standardization for the sorry details). So the US was fortunate that its opponents were usually fighter planes (and in the case of the Japanese, mostly lightly protected) so a battery of six or eight .50s turned out to be perfectly adequate for their needs.

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## pbehn (Nov 6, 2020)

GrumpyOldCrewChief said:


> I don't think I have seen a mention, except in passing, of one of the big reasons the US chose the M2. Production and logistics standardization. Yes, most upper echelon folks knew there were "better" solutions, but also had fears that production or logistics bottlenecks might be leaving fighting outfits with the wrong ammo. Or tools to fix, or whatever else. If everybody uses the same type of item, everybody always gets the right item. As our log tails got better organized, this was less of a real concern, but always remained as a BIG ghost in everybody's thinking. Standardization was viewed by many as a key to large production numbers. As an illustration - was the Sherman a good tank? Maybe, and certainly nowhere near as good, one for one, as many of the German tanks it met. But we could build thousands of them, and keep them in service, because of (relative) standardization. Assurance of meeting the level of performance required, at most times, trumped "best". The M2 performed well enough, often enough, to be the simplest solution. Again, it hadn't the highest RoF, or the highest projectile weight. But, it was the best compromise solution available.
> And don't forget other production issues. If the US wants to use Hisso V cannons in everything, where is that huge number of weapons going to come from? License manufacture is an artform, from initial negotiations, to actual production line problem solving. A whole can of worms that many - right or wrong, better or worse - would not at that time willingly opened.
> 
> Most of what we are discussing here was also known to the production planners back then. If my goal is to present the "fightingest" weapons & force available, I would agree, mostly, with them. We get the Monday Morning Quarterback experience. They didn't have that option.


I think that there was also another aspect to logistics, the amount of investment in production capacity and guns/ rounds of ammunition already made.


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## Glider (Nov 6, 2020)

jmcalli2 said:


> I think it depends on your mission. The British liked that set up, and the USN moved that way too. The USAAC even went with it in the P-61, and remember many of those did not have the 4 x .50cal turret mounted. In many mission though, more ammo may be what you need at the cost of reduced firepower; escort and interception of dive bombers come to mind.
> 
> It's like asking which is a better engine, one that gives you acceleration or one that gives you cruise; are you running the Indy 500 or a 1/4 mile NHRA race?



You certainly have a point in particular on long distance escort missions. That said, the Tempest gave you about 16 seconds of fire which isn't bad and not that many pilots used all their ammunition. You could also point out that a burst from the 4 x 20 would do far more damage than from the 6 x 0.50 so less ammunition would be needed


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## Glider (Nov 6, 2020)

BiffF15 said:


> I think there is room here for a few more variables. First, if instead of 6 x .50s one went with 4 but increased the ammo it would give a commensurate increase in trigger time. Second, I think in combat there is a “it depends”. Reliability would be number one, or in other words knowing that when I squeezed the trigger that the guns would work. I would take reliability as my number one choice, then increased rounds count (longer trigger time / Mk14 type gunsight?) until I became a confident shooter, then would switch to heavier caliber.
> 
> Food for thought.
> 
> ...



As ever good points, but the P51 development went from 4 x 0.5 to 6 x 0.5 they would have done it for a reason, presumably because 4 x 0.5 was lacking. I am not aware of any significant complaints about a lack of 'trigger time' (I do like that phrase) of the P51

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## pbehn (Nov 6, 2020)

Glider said:


> As ever good points, but the P51 development went from 4 x 0.5 to 6 x 0.5 they would have done it for a reason, presumably because 4 x 0.5 was lacking. I am not aware of any significant complaints about a lack of 'trigger time' (I do like that phrase) of the P51


Possibly because even before the P-51B was introduced strafing aircraft on the ground was part of many mission profiles and in that only the number of bullets per second matters because a ground target is only in the gunsight for a fraction of a second.


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## Snowygrouch (Nov 6, 2020)

This may help. From USAAF microfilm report.

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## jmcalli2 (Nov 6, 2020)

Glider said:


> You certainly have a point in particular on long distance escort missions. That said, the Tempest gave you about 16 seconds of fire which isn't bad and not that many pilots used all their ammunition. You could also point out that a burst from the 4 x 20 would do far more damage than from the 6 x 0.50 so less ammunition would be needed


Good points, but weren't most Tempest missions strafing/ground attack? A different issue from air to air; again, it depends upon your mission.


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## jmcalli2 (Nov 6, 2020)

Snowygrouch said:


> This may help. From USAAF microfilm report.
> 
> View attachment 600945
> 
> View attachment 600946


Cool!

One thing to keep in mind: not all 20mm were created equal. The Hispano fired a bigger shell at a higher muzzle velocity and faster or similar rate of fire than the smaller and lighter Mg151/20; The WWII Fighter Gun Debate: Gun Tables

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## pbehn (Nov 6, 2020)

jmcalli2 said:


> Good points, but weren't most Tempest missions strafing/ground attack? A different issue from air to air; again, it depends upon your mission.


from wiki for the HS MkV … Ammunition types available included Semi-Armour Piercing, Incendiary (SAPI) and High Explosive, Incendiary (HEI).[10] Around 42,500 Hispano cannon of various marks were manufactured by Birmingham Small Arms (BSA).

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## jmcalli2 (Nov 6, 2020)

pbehn said:


> from wiki for the HS MkV … Ammunition types available included Semi-Armour Piercing, Incendiary (SAPI) and High Explosive, Incendiary (HEI).[10] Around 42,500 Hispano cannon of various marks were manufactured by Birmingham Small Arms (BSA).


Now, just to add more powder to the charge, consider the US M9 37mm cannon. This was used on late model P-63. It differed from the M4/M10 37mm in that it was a completely different design, being developed from the US Army 37mm AA gun. While it had the same low rate of fire as the M4, it fired a 10% larger shell at 2800 ft/s. The down side was it was really heavy. With that big shell at that high muzzle velocity heavy bombers could be attacked outside the range of defensive fire with a one round kill weapon.
Good thing B-17s, B-24s, and Lancasters didn't have to deal with that!

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## The Basket (Nov 6, 2020)

I British.
I want my 303.

Moving to Korean War and it was quickly apparent that 20mm cannon was the way.

Fast firing 20mm cannon. The Zero in service quickly found out the Wildcat was a tough old bird. The machine guns were just scratching the paint work. The Tempest didn't carry 303s. So the proof is in that pudding.

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## Koopernic (Nov 6, 2020)

BiffF15 said:


> I think there is room here for a few more variables. First, if instead of 6 x .50s one went with 4 but increased the ammo it would give a commensurate increase in trigger time. Second, I think in combat there is a “it depends”. Reliability would be number one, or in other words knowing that when I squeezed the trigger that the guns would work. I would take reliability as my number one choice, then increased rounds count (longer trigger time / Mk14 type gunsight?) until I became a confident shooter, then would switch to heavier caliber.
> 
> Food for thought.
> 
> ...


The most important variable is that 50 caliber gun has less drag in certain circumstances.

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## Shortround6 (Nov 6, 2020)

jmcalli2 said:


> consider the US M9 37mm cannon. This was used on *A* late model P-63



Fixed it 

The M9 cannon was used on _one _P-63 aircraft, as in one plane, not one model or version. 
P-63s from the A-9 on got the US M10 37mm cannon which used the same ammo as the M4 cannon. It fired just a bit faster but used a real belt (disintegrating link) for feeding and held a lot more rounds than the M4 set up.

Confusion comes from the M10 cannon being called the T9 when in development.

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## Shortround6 (Nov 6, 2020)

GrumpyOldCrewChief said:


> I don't think I have seen a mention, except in passing, of one of the big reasons the US chose the M2. Production and logistics standardization



During the 30s the .50 cal (not yet the M2 ?) was used by the air corp, the ground army, the Navy (and naval aviation) and the Marines. 
Using the same receiver and interior parts it was possible to build an aircraft gun or a water cooled AA gun or any other version. The M2 was also possible to convert from left hand to right hand feed with s few parts. Later it was _possible_ to convert the slow firing ground guns to higher rate of fire aircraft guns by changing barrels and a few other parts. not often done. 
The .50 was a barrel burner and light weight aircraft barrels and fast firing guns without 200-300mph cooling breeze was not a good idea. PT boats may have been the only users of high rate of fire guns in surface combat? 

This gave quite an advantage in logistics. The advantage tended to fade during the war with the sheer quantity of war material but the light Navy AA gun (before the 20mm Oerlikon) used the same ammo as some of the Navy aircraft guns (the others were .30 cal) , and the Army aircraft guns and the army ground anti-armor gun (up until about 1940) and AA guns. There may have been different kinds of ammo but each and every one could be fired out of any of the "different" guns should the need arise. Likewise bolts, firing pins, springs, extractors, ejectors and feed parts were all 100% interchangeable. 
The advantage in manufacturing and supply was considerable. 

This may have helped outweigh the disadvantages of the .50 cal.

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## PAT303 (Nov 7, 2020)

Koopernic said:


> The most important variable is that 50 caliber gun has less drag in certain circumstances.



That is true but two Hispano's weighed 100kg yet had the on target effect of 6 Brownings that combined weighed 230kgs, so pluses and minuses for both.


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## pbehn (Nov 7, 2020)

jmcalli2 said:


> Now, just to add more powder to the charge, consider the US M9 37mm cannon. This was used on late model P-63. It differed from the M4/M10 37mm in that it was a completely different design, being developed from the US Army 37mm AA gun. While it had the same low rate of fire as the M4, it fired a 10% larger shell at 2800 ft/s. The down side was it was really heavy. With that big shell at that high muzzle velocity heavy bombers could be attacked outside the range of defensive fire with a one round kill weapon.
> Good thing B-17s, B-24s, and Lancasters didn't have to deal with that!


That was the first job of the escorts, make sure there is no easy shot. They may not have been able to do much about an attacking Me262s speed, other than make sure they had to use all of it and its hard to hit a moving target when you are doing 500MPH yourself.


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## tomo pauk (Nov 7, 2020)

jmcalli2 said:


> Cool!
> 
> One thing to keep in mind: not all 20mm were created equal. The Hispano fired a bigger shell at a higher muzzle velocity and faster or similar rate of fire than the smaller and lighter Mg151/20; The WWII Fighter Gun Debate: Gun Tables



The Hispano II fired at lower RoF than the MG 151/20. In ww2, Hispano V saw serivce in Tempest. 
US Hispano was equivalent of the Hispano II (when worked).

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## jmcalli2 (Nov 7, 2020)

The Basket said:


> I British.
> I want my 303.
> 
> Moving to Korean War and it was quickly apparent that 20mm cannon was the way.
> ...


Wan't the original Typhoon design to have 12 .303s, or have I had too much Balvenie Doublewood tonight?


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## jmcalli2 (Nov 7, 2020)

Shortround6 said:


> Fixed it
> 
> The M9 cannon was used on _one _P-63 aircraft, as in one plane, not one model or version.
> P-63s from the A-9 on got the US M10 37mm cannon which used the same ammo as the M4 cannon. It fired just a bit faster but used a real belt (disintegrating link) for feeding and held a lot more rounds than the M4 set up.
> ...


My bad; I know the M9 was used on the P-63D (the bubble top), but I thought it was on the E and F also.
Thanks for the correction!


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## jmcalli2 (Nov 7, 2020)

pbehn said:


> That was the first job of the escorts, make sure there is no easy shot. They may not have been able to do much about an attacking Me262s speed, other than make sure they had to use all of it and its hard to hit a moving target when you are doing 500MPH yourself.


The Me-262s carried Mk 108 30mm. These had a relatively low muzzle velocity, so you'd have to get closer. The shell was about 40% the size of the M9 37mm, but the rate of fire was 4 times faster and the gun weighed 1/3 as much, so you trade off was heavy shell at long range vs more shells at closer range.
Just a thought: missiles are essentially very big shells at very long range.


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## jmcalli2 (Nov 7, 2020)

Koopernic said:


> The most important variable is that 50 caliber gun has less drag in certain circumstances.


Now, that's an interesting take! Tell me more!


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## jmcalli2 (Nov 7, 2020)

tomo pauk said:


> The Hispano II fired at lower RoF than the MG 151/20. In ww2, Hispano V saw serivce in Tempest.
> US Hispano was equivalent of the Hispano II (when worked).


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## PAT303 (Nov 7, 2020)

jmcalli2 said:


> Now, that's an interesting take! Tell me more!



In regards to drag the Spitfire lost about 7mph because of the cannon barrels poking forward of the wings and blisters covering the receiver mechanism.

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## wuzak (Nov 8, 2020)

Koopernic said:


> The most important variable is that 50 caliber gun has less drag in certain circumstances.





jmcalli2 said:


> Now, that's an interesting take! Tell me more!





PAT303 said:


> In regards to drag the Spitfire lost about 7mph because of the cannon barrels poking forward of the wings and blisters covering the receiver mechanism.



I thought Koopernic was referring to the aerodynamics of the shell for improved ballistics.


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## wuzak (Nov 8, 2020)

jmcalli2 said:


> Now, just to add more powder to the charge, consider the US M9 37mm cannon. This was used on late model P-63. It differed from the M4/M10 37mm in that it was a completely different design, being developed from the US Army 37mm AA gun. While it had the same low rate of fire as the M4, it fired a 10% larger shell at 2800 ft/s. The down side was it was really heavy. With that big shell at that high muzzle velocity heavy bombers could be attacked outside the range of defensive fire with a one round kill weapon.
> Good thing B-17s, B-24s, and Lancasters didn't have to deal with that!




They only had to deal with 20mm, 30mm, 37mm (used in Bf 110 and Ju 88 for attacking bombers BK 3,7 - Wikipedia), 50mm (in limited use Rheinmetall BK-5 - Wikipedia), rockets, flak and bombs!

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## PAT303 (Nov 8, 2020)

The Basket said:


> I British.
> I want my 303.



If you read through the battle of Britain thread a very large proportion of Bf109's didn't have armour fitted so the .303's were still and were very effective.


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## Koopernic (Nov 8, 2020)

jmcalli2 said:


> Now, that's an interesting take! Tell me more!


The British experience with the Hispano on the Typhoon fighter was that the 4 Hispano Mk 2 guns slowed the aircraft down significantly. Fairings were developed but these only lessened the significant speed loss. The Hispano Mk 2 was an enormous weapon almost twice the length of the 50 caliber M2. It was as long as the long barreled german 30mm Mk 103.

The solution was to shorten the barrel and surrender some velocity and these Hispano Mk V appeared in the tempest.

Typhoon probably could have carried 8 x 50 calibre M2 Browning fully in the wings.

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## PAT303 (Nov 8, 2020)

wuzak said:


> I thought Koopernic was referring to the aerodynamics of the shell for improved ballistics.



He did say .50 Cal gun so I assumed he was talking about the browning's being flush with the leading edge.

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## tomo pauk (Nov 8, 2020)

jmcalli2 said:


> Wan't the original Typhoon design to have 12 .303s, or have I had too much Balvenie Doublewood tonight?



Yes, 12 .303s. FWIW, the Hurricane IIB also carried 12 Brownings.

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## tomo pauk (Nov 8, 2020)

Koopernic said:


> The British experience with the Hispano on the Typhoon fighter was that the 4 Hispano Mk 2 guns slowed the aircraft down significantly. Fairings were developed but these only lessened the significant speed loss.



From here:
_Cleaning up of Typhoon 1._
_ Level speeds of production aircraft:- Full tests have been done at Gloster on the level speeds of 4 recent production aircraft of average finish. The maximum level speeds obtained were:_

_Typhoon 1A. R.7914 397.5 m.p.h. at 20,500 ft. F.S. 385 m.p.h. at 8,400 ft. M.S. 
Typhoon 1A. R. 7869 396.5 m.p.h. at 20,100 ft. F.S. 379 m.p.h. at 8,000 ft. M.S. 
Typhoon 1B. R. 8650 393 m.p.h. at 20,800 ft. F.S. 382 m.p.h. at 8,800 ft. M.S. 
Typhoon 1B. R. 8636 392 m.p.h. at 20,000 ft. F.S. 379 m.p.h. at 8,200 ft. M.S. _

1A being the 12 Brownings version, 1B being with 4 Hispano IIs. Under 5 mph speed loss on average for the cannon-armed Typhoon is hardly significant.



> The Hispano Mk 2 was an enormous weapon almost twice the length of the 50 caliber M2. It was as long as the long barreled german 30mm Mk 103.
> The solution was to shorten the barrel and surrender some velocity and these Hispano Mk V appeared in the tempest.



About the size of Hisso II - the 'no free lunch' rule applies. When introduced, it was the most powerful airborne weapon intended to fight other aircraft. It was not enormous, 4 fitted in the thin wing of Spitfire.
Shortening of the cannons' barrels was not something Typhoon needed, it have had more than enough power to cater for that. Typhoon needed a number of changes that were not related to armament in order to succeed.

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## jmcalli2 (Nov 8, 2020)

PAT303 said:


> In regards to drag the Spitfire lost about 7mph because of the cannon barrels poking forward of the wings and blisters covering the receiver mechanism.


Now that you say it, I did know that but completely forgot it.


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## jmcalli2 (Nov 8, 2020)

wuzak said:


> They only had to deal with 20mm, 30mm, 37mm (used in Bf 110 and Ju 88 for attacking bombers BK 3,7 - Wikipedia), 50mm (in limited use Rheinmetall BK-5 - Wikipedia), rockets, flak and bombs!



The Mk 103 30mm was akin to the 37mm M9 in that it had a high muzzle velocity, but, like the M9, it was large and heavy. Germany was stuck with a majority of small fighters (109 & 190) or some clumsy fighters (110, 210, 410) for the most part. As a weapons system a P-63D would have been a problem for the USAAF. Just my opinion.


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## jmcalli2 (Nov 8, 2020)

tomo pauk said:


> Yes, 12 .303s. FWIW, the Hurricane IIB also carried 12 Brownings.


 And some carried the Vickers 40mm for ground attack. I remember buying the 1/48th scale model (Monogram I think, maybe Revel) as a kid, and trying to figure out if I could put all the armament options on the plane at the same time! LOL


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## Koopernic (Nov 9, 2020)

tomo pauk said:


> From here:
> _Cleaning up of Typhoon 1._
> _ Level speeds of production aircraft:- Full tests have been done at Gloster on the level speeds of 4 recent production aircraft of average finish. The maximum level speeds obtained were:_
> 
> ...



"Under 5 mph speed loss on average for the cannon-armed Typhoon is hardly significant."

5mph is not significant unless the 392-393mph Typhoon IB comes into contact with the 408-410mph Fw 190A5 at 20,000ft. Fortunately for the RAF the Sabre engine's power improved.
Speed loss occurs in trifles: gun ports, wheel well covers., retractable tail wheels, gaps in the radiator etc.

The barrel length of the Hispano II became more of an issue on the Tempest (due to its slimmer wings and higher targeted speed) and the Spitfire F22/F24 series which both needed the short barrelled Hispano V.

The gun was troublesome in wing installations. The US version which used a slightly different cartridge never became reliable enough to put into service despite millions of rounds of ammunition being produced.




"

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## pbehn (Nov 9, 2020)

PAT303 said:


> In regards to drag the Spitfire lost about 7mph because of the cannon barrels poking forward of the wings and blisters covering the receiver mechanism.


The Typhoon had a lot more power and a lot more, drag in part because of its thick wings but those wings could hold the cannon without having blisters.

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## tomo pauk (Nov 9, 2020)

Koopernic said:


> "Under 5 mph speed loss on average for the cannon-armed Typhoon is hardly significant."
> 
> 5mph is not significant unless the 392-393mph Typhoon IB comes into contact with the 408-410mph Fw 190A5 at 20,000ft. Fortunately for the RAF the Sabre engine's power improved.
> Speed loss occurs in trifles: gun ports, wheel well covers., retractable tail wheels, gaps in the radiator etc.



Most of the manufacturers were allowed for 3% variation on speed for production version of ww2 fighters. At ~400 mph that means 12 mph difference between the best and worst performing 'specimen' - thus 5 mph speed loss due to massive increase of firepower was nothing. 
Speed losses do happen on trivialities, however Typhoon was loosing a lot because of it's wing being of big TtC ratio and of outdated profile.



> The barrel length of the Hispano II became more of an issue on the Tempest (due to its slimmer wings and higher targeted speed) and the Spitfire F22/F24 series which both needed the short barrelled Hispano V.



Who said that Tempest or Spitfire F22/24 needed the short barreled Hispano V?



> The gun was troublesome in wing installations. The US version which used a slightly different cartridge never became reliable enough to put into service despite millions of rounds of ammunition being produced.



Hispano worked in Hurricane and Typhoon. After initial problems, it also worked on Spitfire. 
US Hispano have had a problem both with ammo and chamber length.
Main problem with Hispano was that it was lagging behind Oerlikon's cannons for several years.


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## Koopernic (Nov 10, 2020)

tomo pauk said:


> Most of the manufacturers were allowed for 3% variation on speed for production version of ww2 fighters. At ~400 mph that means 12 mph difference between the best and worst performing 'specimen' - thus 5 mph speed loss due to massive increase of firepower was nothing.
> Speed losses do happen on trivialities, however Typhoon was loosing a lot because of it's wing being of big TtC ratio and of outdated profile.
> 
> Who said that Tempest or Spitfire F22/24 needed the short barreled Hispano V?
> ...



Why did Supermarine fit shortened Hispano V to the Spitfire F22/F24? We know that Spitfires from the Mk XVII down had handling problems with 4 full length Hispano 2
Why did Hawker convert the Tempest V from Hispano 2 to Hispano 5. Hint because long barrel units were 5 mph slower at the same altitude and nearly 7 at optimum altitude. Had the Hispano V been available they wuld have used it in a heat beat.

As far as scatter goes I don't accept it. These were airframes that were carefully inspected for development testing. We have a consistent advantage to the 12 x Browning Typhoon in speed over the 4 Hispano V Typhoon.

If it wasn't necessary why did the RAF, Hawkers, RAE waste their time putting in an weapon with inferior ballistics? The Hispano V lost 5% muzzle velocity, 10% kinetic energy and about the same 10% loss in armour penetration.

The weapon clearly was powerful but gas operated mechanisms are known to be finicky to develop and maintain.

The Oerlikon Mechanism API mechanism and that of the MG151 were recoil operated. The non locking bolt was heavy but served to buffer recoil which helped keep installed weight down. The MG151 was designed for synchronisation from the start.

"


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## tomo pauk (Nov 10, 2020)

Koopernic said:


> Why did Supermarine fit shortened Hispano V to the Spitfire F22/F24? We know that Spitfires from the Mk XVII down had handling problems with 4 full length Hispano 2
> Why did Hawker convert the Tempest V from Hispano 2 to Hispano 5. Hint because long barrel units were 5 mph slower at the same altitude and nearly 7 at optimum altitude. Had the Hispano V been available they wuld have used it in a heat beat.



Supermarine and Hawker fitted the Hispano V on their fighter because the Hispano V was now available, and Hispano II was being phased out production. It offered 750 rd/min* vs. 600 rd/min for the Mk.II - so basically it was a firepower of 5 Mk.IIs for weight penalty of 3.5 Mk.IIs.

Problem with, typically, Spitfire V lugging around 4 cannons was lack of engine power for such a heavy battery. Similar problem was shared by many P-40s, P-39s and Fw 190As.



> As far as scatter goes I don't accept it. These were airframes that were carefully inspected for development testing. We have a consistent advantage to the 12 x Browning Typhoon in speed over the 4 Hispano V Typhoon.



The no free lunch rule applies as ever - 5 mph speed loss was diminutive price to pay for huge increase of firepower. The Fw 190A lost same amount of speed when it swapped the fuselage LMGs with HMGs, for a very small % of increase of total firepower. Some aircraft required gondolas when wanting to go from 1 cannon to 2 or 3, with a major performance loss.



> If it wasn't necessary why did the RAF, Hawkers, RAE waste their time putting in an weapon with inferior ballistics? The Hispano V lost 5% muzzle velocity, 10% kinetic energy and about the same 10% loss in armour penetration.



Armour penetration & kinetic energy was not high on the RAF's list. Increase of rate of fire, while saving close to 80 lbs per 4-barreled installation, was high on the priority list. Muzzle velocity of 840 m/s was still higher than what German, Soviet or Japanese 20mm cannons offered.



> The weapon clearly was powerful but *gas operated mechanisms are known to be finicky to develop and maintain.*



(my bold)
Don't post misinformation.



> The Oerlikon Mechanism API mechanism and that of the MG151 were recoil operated. The non locking bolt was heavy but served to buffer recoil which helped keep installed weight down. The MG151 was designed for synchronisation from the start.



Source for MG 151 having a non-locking bolt? What kept the installed weight down for MG 151 was that it was not firing a really powerful cartridge vs. what Hispano used.

*in a lot of places the 800 rd/min is quoted for Hisso V


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## Snautzer01 (Nov 10, 2020)

Waffen Revue, German weapons explained in detail MG151

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## A.G. Williams (Nov 10, 2020)

Snautzer01 said:


> Waffen Revue, German weapons explained in detail MG151



That isn't the 20 mm MG 151, it's the 7.9 mm MG 15 - no relation.


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## Snautzer01 (Nov 10, 2020)

ok what does mg 151/20 stands for then?

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## Vincenzo (Nov 10, 2020)

Probably Williams not noticed what happened after he opened the link
after a moment you open the link show the MG 15 article, because of imagines open later of the page

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## Shortround6 (Nov 10, 2020)

Yes the Hispano's were big.
Hispano's were a hybrid gun. They used a combination of gas and recoil. The shorter lighter barrel helped with the increase in the rate of fire.

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## A.G. Williams (Nov 10, 2020)

Snautzer01 said:


> ok what does mg 151/20 stands for then?



Oh, OK - the link opened straight into MG 15 for me.

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## A.G. Williams (Nov 10, 2020)

Shortround6 said:


> Hispano's were a hybrid gun. They used a combination of gas and recoil. The shorter lighter barrel helped with the increase in the rate of fire.



It was a hybrid but with a combination of gas and blowback. Gas tapped from the barrel was used to unlock the breech, after which gas pressure in the barrel blew the fired case backwards and out of the gun.

The rate of fire was determined by a number of factors, barrel length wasn't that significant.


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## jmcalli2 (Nov 10, 2020)

Koopernic said:


> "Under 5 mph speed loss on average for the cannon-armed Typhoon is hardly significant."
> 
> 5mph is not significant unless the 392-393mph Typhoon IB comes into contact with the 408-410mph Fw 190A5 at 20,000ft. Fortunately for the RAF the Sabre engine's power improved.
> Speed loss occurs in trifles: gun ports, wheel well covers., retractable tail wheels, gaps in the radiator etc.
> ...


You also need a heavier structure to support the heavier recoil. In the P-39/63 the huge 37mm was supported by the center of the aircraft; the plane was designed around it. The German Mk 101-103 with their high muzzle velocity posed the structure problem; one of the reasons for the Mk 108.

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## jmcalli2 (Nov 10, 2020)

Snautzer01 said:


> ok what does mg 151/20 stands for then?
> 
> View attachment 601430


The original gun was the Mg 15 for 15mm. The design was modified with a new chamber and barrel and became the 20mm Mg 15/20.


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## jmcalli2 (Nov 10, 2020)

Shortround6 said:


> View attachment 601455
> 
> 
> Yes the Hispano's were big.
> Hispano's were a hybrid gun. They used a combination of gas and recoil. The shorter lighter barrel helped with the increase in the rate of fire.


Hispanos were anything but short: it was 93 aches long. The MgFF was 53 inches long, the M4 Browning 37mm was 89 inches long, and the Browning .50 cal was 65 inches long.


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## tomo pauk (Nov 10, 2020)

jmcalli2 said:


> The original gun was the Mg 15 for 15mm. The design was modified with a new chamber and barrel and became the 20mm Mg 15/20.



MG 15 was s LMG, for 7.92mm ammo.
MG 151/15 was a cannon for 15mm ammo. MG 151/20 was the 20mm version.

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## Admiral Beez (Nov 10, 2020)

Clayton Magnet said:


> The 20mm Hispano and Browning M2 had similar rates of fire, and similar muzzle velocities.


Yes, speed and frequency to target may be similar, but unlike the solid lead of the .50 cal, the 20mm explodes on impact.


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## jmcalli2 (Nov 10, 2020)

tomo pauk said:


> MG 15 was s LMG, for 7.92mm ammo.
> MG 151/15 was a cannon for 15mm ammo. MG 151/20 was the 20mm version.


Thanks for correcting me!

I blame a coffee deficiency.


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## A.G. Williams (Nov 10, 2020)

Admiral Beez said:


> Yes, speed and frequency to target may be similar, but unlike the solid lead of the .50 cal, the 20mm explodes on impact.


A bit of nit-picking: the standard .50 cal ball didn't have a lead core, it had a steel one in a thin lead sleeve. From 1944 onwards, the favoured bullet type for fighter aircraft was the M8 API; this had a hardened steel armour-piercing core with a quantity of incendiary material in the jacket tip. It was common to make every fourth or fifth round an M20 API-T (tracer). For bomber defence, the .50 often used the M21 "Headlight" tracer; it had been discovered that attacking Luftwaffe pilots could be distracted by seeing the tracers coming towards them, so the M21 was designed to have a big, bright tracer which could easily be seen from the front.

The standard RAF 20mm Hispano belt make-up from mid-war onwards was two HEI followed by two SAPI (semi-armour-piercing-incendiary). The HEI had a fuze with a slight delay, to ensure that it exploded inside the target rather than on the surface. The SAPI shells used the same shell body as the HEI, but were filled with a large quantity of incendiary material and were given a penetrating steel cap instead of a fuze; the incendiary was ignited by the shock of impact. They both worked pretty well, once the early problems with over-sensitive fuzes were dealt with (the Luftwaffe had the same problem with their 20mm HE).

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## tomo pauk (Nov 10, 2020)

A.G. Williams said:


> <>



Tony, since you're here - is there a manual for the Hispano V available for easy download?


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## Greyman (Nov 10, 2020)

tomo pauk said:


> Supermarine and Hawker fitted the Hispano V on their fighter because the Hispano V was now available, and Hispano II was being phased out production. It offered 750 rd/min* vs. 600 rd/min for the Mk.II - so basically it was a firepower of 5 Mk.IIs for weight penalty of 3.5 Mk.IIs.



150 rounds/min faster, 30 lb lighter, and greater simplicity of installation were the main 'selling' points. The loss of 65 ft/sec in muzzle velocity was a small price to pay for these improvements -- especially with gyro sights.


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## tomo pauk (Nov 10, 2020)

Greyman said:


> 150 rounds/min faster, 30 lb lighter, and greater simplicity of installation were the main 'selling' points. The loss of 65 ft/sec in muzzle velocity was a small price to pay for these improvements -- especially with gyro sights.



Agreed. A combination of heavy shell, very good RoF, still very good MV and reasonable weight were strong selling points of the Hisso V.
Seems like the weight difference for a single gun was 8 kg - around 20 lb.


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## Admiral Beez (Nov 10, 2020)

Were all WW2 aircraft cannons metric?


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## Greyman (Nov 10, 2020)

A couple of the heavier British cannon (Vickers 'S', Mollins 'M') are sometimes referred to as 2pdr and 6pdr respectively -- but I think the official designations stuck with metric.


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## Shortround6 (Nov 10, 2020)

A.G. Williams said:


> It was a hybrid but with a combination of gas and blowback. Gas tapped from the barrel was used to unlock the breech, after which gas pressure in the barrel blew the fired case backwards and out of the gun.
> 
> The rate of fire was determined by a number of factors, barrel length wasn't that significant.



Thank you for the correction. 

I think I was confused by the recoil absorbing mountings. The entire gun recoils with each shot and is returned to the forward position before the next one but the guns movement doesn't do anything to operate the action. Except that the belt feed guns use the movement of the gun to power the belt feed mechanism. 
The Spring mounts do lessen the recoil impacts on the airframe. 

Lighter reciprocating parts (or entire gun) would help the rate of fire?


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## Koopernic (Nov 10, 2020)

T


tomo pauk said:


> Supermarine and Hawker fitted the Hispano V on their fighter because the Hispano V was now available, and Hispano II was being phased out production. It offered 750 rd/min* vs. 600 rd/min for the Mk.II - so basically it was a firepower of 5 Mk.IIs for weight penalty of 3.5 Mk.IIs.
> 
> Problem with, typically, Spitfire V lugging around 4 cannons was lack of engine power for such a heavy battery. Similar problem was shared by many P-40s, P-39s and Fw 190As.
> 
> ...



The UK deployed 3 versions of their implementation of the Hispano: the Mk I (on the Hurricane) and Mk II (On Typhoon, Spitfire and early Tempest) and Mk V which was the short barrel version of the gun on the Tempest and Spitfire F22 and F24.

Your claim is that shortening the barrel was done for reasons of increasing rate of fire rather than aerodynamics. Apart from contradicting a expert in this thread there are two arguments against this:
1 The Full length US Hispano, All 2.45m of it, known as the M1 achieved a cadence of 700rpm which is 100rpm greater than the full length British versions of the same time. I'm not even sure what the ROF of the Hispano 2 was, it seems to have increased. It may have been greater than 600. The latter US M2/M3 versions were shortened like the Hispano V.

2 Unlike the Oerlikon the Hispano fired from a locked breech bolt. When the round being fired eventually passed a gas port which channelled gas back to a piston that was used to unlock unlocked the bolt. Residual gas pressure then ejected the spent cartridge casing against the bolt.

By contrast the Oerlikon's API mechanism fired while the bolt was moving forward, the mass of the bolt had to be high to slow the bolt enough and arrest the the recoil and this created a trade of between cadence, muzzle velocity and weight. 

The Mauser MG151 used a short recoil. The bolt was locked with the barrel like the Hispano, however after firing the motion of the barrel unlocked the bolt after a short recoil (instead of gas). The barrel then stops quickly but the bolt continues backward (via inertia and residual pressure) to allow extraction and reloading. This mechanism has less of a trade of but it also has the advantage of firing from a closed bolt that helps synchronisation.

The Hispano mechanism should have been suitable for synchronisation.

The Hispano was thus not dependant on the a heavy bolt, as in Oerlikon and Mk 108 because the locking mechanism meant the round left the barrel before the lightweighed bolt opened since it remained locked till the gas port was exposed.

*The Gas channels in the Hispano represent an area that needs cleaning because it is vulnerable to fouling as well as being a complication.*

The long barrelled Mauser Mk 103 used a gas mechanism to unlock the bolt but used barrel recoil for extraction.
The German 3.7cm FLAK 18,36 & 37 used it as did the highly refined 3.7cm FLAK 43.

Incidentally the full length HS 820 (2.45m) fires at 1000 rpm using a gas mechanism. (not revolver)


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## Greyman (Nov 11, 2020)

Koopernic said:


> The UK deployed 3 versions of their implementation of the Hispano: the Mk I (on the Hurricane) and Mk II (On Typhoon, Spitfire and early Tempest) and Mk V which was the short barrel version of the gun on the Tempest and Spitfire F22 and F24.



I think the Mk.I might have been found on any of the early Hispano-carrying aircraft. Though by the time any of the (British) Hispano aircraft started seeing any real service Hispano Mk.II production was well underway.




Shortround6 said:


> Lighter reciprocating parts (or entire gun) would help the rate of fire?



I don't think there was much lightening done in that department -- most weight saving was in the barrel and body -- but the modifications to the gas plug might have been all that was required. The buffer spring was strengthened as well.

The original French gun (and British copy, the Mk.I) fired at about 700 rounds/minute, but after various trials in 1939 it was found that reliability and breakages were greatly improved if the rate of fire was kept down to about 600 rounds/minute -- so this was specified in the Mk.II gun.

The same thing played out in the development of the Mk.V -- initial rate of fire was 820 rounds/min, but this was toned down to 750.

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## ThomasP (Nov 11, 2020)

I ran across 2 UK manuals for the 20mm Mk I and Mk II a number of years ago, and the stated ROFs were the same for both. One UK manual listed 650-675 rpm when using the 60 round drum, and 590-620 rpm when using the belt feed. The other UK manual listed 650 rpm. The US manual TM 9-227 for the 20mm M1 and M2 lists ROFs of 600-700 rpm. The US manual TM 9-229 for the 20mm M3 lists 650-800 rpm. The US manual TM 9-2006 for the 20mm M24 (M3 modified for electrically fired primer ammunition) lists 700-800 rpm.

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## A.G. Williams (Nov 11, 2020)

tomo pauk said:


> Tony, since you're here - is there a manual for the Hispano V available for easy download?



I have one in book form for the Mk I and Mk II, but not the Mk V.


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## tomo pauk (Nov 11, 2020)

Koopernic said:


> Your claim is that shortening the barrel was done for reasons of increasing rate of fire rather than aerodynamics. Apart from contradicting a expert in this thread...



Quote my post where I'm contradicting an expert in this thread with regard to the connection between barrel length and rate of fire on Hispano.



> ... there are two arguments against this:
> 1 The Full length US Hispano, All 2.45m of it, known as the M1 achieved a cadence of 700rpm which is 100rpm greater than the full length British versions of the same time. I'm not even sure what the ROF of the Hispano 2 was, it seems to have increased. It may have been greater than 600. The latter US M2/M3 versions were shortened like the Hispano V.
> 
> 2 Unlike the Oerlikon the Hispano fired from a locked breech bolt. When the round being fired eventually passed a gas port which channelled gas back to a piston that was used to unlock unlocked the bolt. Residual gas pressure then ejected the spent cartridge casing against the bolt.
> By contrast the Oerlikon's API mechanism fired while the bolt was moving forward, the mass of the bolt had to be high to slow the bolt enough and arrest the the recoil and this created a trade of between cadence, muzzle velocity and weight.



1 - 700 rd/min for Hispano I/II is cherry-picking the best scenario. This is what Tony Williams says (from here; my bold):
_Compared with other Second World War 20 mm aircraft cannon, the Hispano was a powerful and effective gun, but only averagely fast-firing and unusually long and heavy. *Its weaknesses were addressed in the late-war Mk V, shortened, lightened and speeded-up from 600 to 750 rpm. *_

2 - Nobody is disputing that.



> The Mauser MG151 used a short recoil. The bolt was locked with the barrel like the Hispano, however after firing the motion of the barrel unlocked the bolt after a short recoil (instead of gas). The barrel then stops quickly but the bolt continues backward (via inertia and residual pressure) to allow extraction and reloading. This mechanism has less of a trade of but it also has the advantage of firing from a closed bolt that helps synchronisation.



So, after all the bolt was locked on MG 151 vs. your claim (my underscore):
_The Oerlikon Mechanism API mechanism and that of the MG151 were recoil operated. The non locking bolt was heavy but served to buffer recoil which helped keep installed weight down. _



> The Gas channels in the Hispano represent an area that needs cleaning because it is vulnerable to fouling as well as being a complication.



Gas tubes, while not being complicated at all, were there so the cannon can actually operate, while giving a substantial increase of RoF vs. then-current mainstream big Oerlikon. In other words: no gas channels = no Hispano cannon.
Everyone knew that gas tubes need to be cleaned, it was not rocket science even in 1930s.


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## A.G. Williams (Nov 11, 2020)

Shortround6 said:


> Lighter reciprocating parts (or entire gun) would help the rate of fire?


A combination of lighter reciprocating parts with stronger (or extra) recoil springs is the universal way to increase RoF. With gas operation (including the Hispano) a lot can be done with the location and size of the gas port: the closer it is to the chamber, the faster the bolt will unlock.


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## A.G. Williams (Nov 11, 2020)

Koopernic said:


> T
> 
> The Hispano mechanism should have been suitable for synchronisation.



It wasn't though, because it was designed to fire from an open bolt. The only one of the Hispano 404-based family which could be synchronised was the US M24, as that had electrical priming (like the MG 151/20E).


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## Shortround6 (Nov 11, 2020)

Greyman said:


> The original French gun (and British copy, the Mk.I) fired at about 700 rounds/minute, _but after various trials in 1939 it was found that reliability and breakages were greatly improved if the rate of fire was kept down_ to about 600 rounds/minute -- so this was specified in the Mk.II gun.



This was a choice some countries made for several different guns. Slower rate of fire for increased reliability and/or durability. Sometimes increased rate of fire was chosen instead. It rather depended on the country's "standard" for reliability and/or durability. Sometimes modifications in the form of redesigned-stronger parts or improved materials (alloys/heat treating) allowed for later increases in rates of fire in later guns. 
Since the acceptable number of jams and broken parts per 1000 (or 10,000) rounds fired is seldom known in popular books it does make comparison difficult. 
This is something that delayed the introduction of the 1050-1200rpm .50 cal Browning machinegun in US service. Many of the early development models could not reach (some by a rather large margin) the desired reliability standard.

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## Koopernic (Nov 11, 2020)

A.G. Williams said:


> A combination of lighter reciprocating parts with stronger (or extra) recoil springs is the universal way to increase RoF. With gas operation (including the Hispano) a lot can be done with the location and size of the gas port: the closer it is to the chamber, the faster the bolt will unlock.



if the lighter less powerful MG151/20 round had of been fired from a Hispano style mechanism what weight reduction and what ROF increase might have been possible? is there a rule, like an inverse of say momentum decrease?


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## jmcalli2 (Nov 11, 2020)

A.G. Williams said:


> A bit of nit-picking: the standard .50 cal ball didn't have a lead core, it had a steel one in a thin lead sleeve. From 1944 onwards, the favoured bullet type for fighter aircraft was the M8 API; this had a hardened steel armour-piercing core with a quantity of incendiary material in the jacket tip. It was common to make every fourth or fifth round an M20 API-T (tracer). For bomber defence, the .50 often used the M21 "Headlight" tracer; it had been discovered that attacking Luftwaffe pilots could be distracted by seeing the tracers coming towards them, so the M21 was designed to have a big, bright tracer which could easily be seen from the front.
> 
> The standard RAF 20mm Hispano belt make-up from mid-war onwards was two HEI followed by two SAPI (semi-armour-piercing-incendiary). The HEI had a fuze with a slight delay, to ensure that it exploded inside the target rather than on the surface. The SAPI shells used the same shell body as the HEI, but were filled with a large quantity of incendiary material and were given a penetrating steel cap instead of a fuze; the incendiary was ignited by the shock of impact. They both worked pretty well, once the early problems with over-sensitive fuzes were dealt with (the Luftwaffe had the same problem with their 20mm HE).



Just remembered I had these from the PT boat exhibit at the USS Massachusetts. I apologize for the low res pics; I lost many from this trip and had to download low res version I had posted.

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## A.G. Williams (Nov 11, 2020)

Koopernic said:


> if the lighter less powerful MG151/20 round had of been fired from a Hispano style mechanism what weight reduction and what ROF increase might have been possible? is there a rule, like an inverse of say momentum decrease?


It's impossible to say - the devil is in the detail.

Anyway, weight comparisons between the Hispano and MG 151/20 are complicated. A couple of extracts from my new book (next year) 

On the MG 151/20: "The gun weighed 42 kg including not just the integral belt feed but also the electrical charging device and electric trigger, without which the gun weighed 36-37 kg. It had a cyclic rate of 700 rpm."

On the US Hispano: "The detailed weight breakdown for the AN-M2 is interesting, as the gun's construction was unusually modular. It weighs 46.3 kg as a bare gun, but the muzzle brake (not used with belt feed) weighs 2.1 kg, the front mounting adapter between 3.4 and 6.4 kg depending on the model, the electric trigger and sear mechanism 0.8 kg, the hydraulic charger 1.2 kg, and the ammunition feed 10 kg (60-round drum) or 8.4 kg (belt feed drive), giving a total weight of 60-67 kg depending on the feed mechanism and the mounting adapter. The mounting or support cradle would be additional to this."

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## tomo pauk (Nov 11, 2020)

A.G. Williams said:


> A couple of extracts from my new book (*next year*)



I've heard that 2021. will be a good year

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## Koopernic (Nov 11, 2020)

A.G. Williams said:


> It's impossible to say - the devil is in the detail.
> 
> Anyway, weight comparisons between the Hispano and MG 151/20 are complicated. A couple of extracts from my new book (next year)
> 
> ...



How long did it take to "charge" the gun if it jammed due to a failure to extract, fire or load? WW2 fighter pilot anecdotes are full of stories of quarries that escaped due to a jamed guns.

Also could the jam be detected and the charge initiated automatically? For instance if the firing trigger was pressed and a timer detects a failure to cycle within a certain amount of time could the charging be initiated without pressing a separate button?

The hydraulic charging for the US Hispanic suggests that a solenoid valve opens a hydraulic line to charge the gun (or all guns simultaneously) when a button is pressed.
Electrical system possibly simpler but possibly slower. The Germans faced copper shortages so wonder if they used aluminium coils.


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## A.G. Williams (Nov 12, 2020)

Koopernic said:


> How long did it take to "charge" the gun if it jammed due to a failure to extract, fire or load? WW2 fighter pilot anecdotes are full of stories of quarries that escaped due to a jamed guns.
> 
> Also could the jam be detected and the charge initiated automatically? For instance if the firing trigger was pressed and a timer detects a failure to cycle within a certain amount of time could the charging be initiated without pressing a separate button?
> 
> ...



I don't have any specific information about charging time, but I expect it would be fast. It was obviously not all that important, however, as omitting the charger was one of the weight-saving measures adopted for the Mk V. The guns were loaded and cocked on the ground.

In those pre-electronic days I don't believe there would have been any automatic detection or rectification of firing problems.

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## Brooke (Nov 12, 2020)

grampi said:


> If you were a fighter pilot in WWII, would you rather have the high rate of fire of the 50 cal, or the hitting power of the 20mm? I personally feel the 50 cal was plenty hard hitting enough to take out ANY aircraft, and its high rate of fire made it even more effective...the slow rate of fire for the 20mm meant you had to be a much better marksman...



In the late 1950s I was in the Air Scouts and we met a Moffett Field Naval Air Station in Mountain View, California. At one of the meetings at the side of an F-8 Crusader jet we were told how it had shot itself. For gunnery practice a barge was used as a target while being towed, i.e. a moving target. The F-8 would dive at the target while firing the forward facing .50 cal guns, continue the dive, level out and fly over the target. The problem was the plane got ahead of the bullets which hit the F-8. This was the motivation to switch to 20 mm. It was not related to rate of fire but rather to get faster bullets.

While studying W.W.II torpedoes it became oblivious that when the probability of a hit goes down as the travel time of the weapon goes up. I maintain that dumb weapons fail to work when the travel time is too long. This applies to torpedoes, big guns, bombs, &Etc.
See: Torpedoes


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## swampyankee (Nov 12, 2020)

Brooke said:


> In the late 1950s I was in the Air Scouts and we met a Moffett Field Naval Air Station in Mountain View, California. At one of the meetings at the side of an F-8 Crusader jet we were told how it had shot itself. For gunnery practice a barge was used as a target while being towed, i.e. a moving target. The F-8 would dive at the target while firing the forward facing .50 cal guns, continue the dive, level out and fly over the target. The problem was the plane got ahead of the bullets which hit the F-8. This was the motivation to switch to 20 mm. It was not related to rate of fire but rather to get faster bullets.
> 
> While studying W.W.II torpedoes it became oblivious that when the probability of a hit goes down as the travel time of the weapon goes up. I maintain that dumb weapons fail to work when the travel time is too long. This applies to torpedoes, big guns, bombs, &Etc.
> See: Torpedoes



From all sources I've seen, the Crusader was never equipped with 0.5 in machine guns; the USN stopped using those as main armament on its aircraft when all its jets had straight wings. There was at least one aircraft that shot itself, which was an F11F Tiger. If I remember, its guns were fired while it was in a shallow climb, then the pilot transitioned to a shallow dive. Alas, at least one or two of the 20 mm shells trajectory intersected with the aircraft's flight path. The FJ-1 Fury, FH Phantom, and the F6U Turd Pirate were the last USN fighters armed with 0.5 in guns; the F2H Banshee, F9F Panther/Cougar, and FJ-2 Fury (which had approximately nothing in common with the FJ-1 Fury) all had 20 mm guns.

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## gomwolf (Nov 13, 2020)

US Ballistic Research Laboratories tested some WW2 fire arms in 1947. Title of the reprot is "Airplane Vulnerability and Overall Armament Effectiveness".
They tested 50cal, 60cal(US copied MG151/15), 20mm Hispano, 3cm MK108, 37mm M4.
I am quite sure you will find your own conclusion after read this report.

Personally I believe bigger HE shell is more effective to aircraft. Cuz it can destroy aircraft's structure itself even if shell didn't hit the vital parts.


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## A.G. Williams (Nov 13, 2020)

Brooke said:


> In the late 1950s I was in the Air Scouts and we met a Moffett Field Naval Air Station in Mountain View, California. At one of the meetings at the side of an F-8 Crusader jet we were told how it had shot itself. For gunnery practice a barge was used as a target while being towed, i.e. a moving target. The F-8 would dive at the target while firing the forward facing .50 cal guns, continue the dive, level out and fly over the target. The problem was the plane got ahead of the bullets which hit the F-8. This was the motivation to switch to 20 mm. It was not related to rate of fire but rather to get faster bullets.



Aircraft did occasionally shoot themselves down, either by overtaking their projectiles and flying into them, or (more often, I think) by ricochets bouncing back into their flight path after a ground strafing run. Some TP projectiles were made frangible specifically to remove the latter risk - they shattered on impact with the ground. 

However, that had nothing to do with the choice of armament calibre. At the end of WW2 the USAAF's preferred ammunition for future fighter armament was the .60 cal derived from a very high-velocity experimental anti-tank rifle round. Prototypes of both the 1950s revolver cannon (which later became the M39) and the M61 Vulcan rotary were made in this calibre, but dropped in favour of necking the case up to 20 mm, as obtaining the blast effect of a cannon shell was recognised as being worth losing some velocity to obtain.


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## A.G. Williams (Nov 13, 2020)

Brooke said:


> While studying W.W.II torpedoes it became oblivious that when the probability of a hit goes down as the travel time of the weapon goes up. I maintain that dumb weapons fail to work when the travel time is too long. This applies to torpedoes, big guns, bombs, &Etc.
> See: Torpedoes



That is clearly correct, as the shorter the flight time the easier it is to hit targets, and it did for a while drive a USAAF obsession with maximising the muzzle velocity of aircraft guns. However, it was eventually realised that explosive cannon shells were more important. No other air force - and not even the USN - questioned the superiority of cannon fire over MGs.


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## Koopernic (Nov 13, 2020)

A.G. Williams said:


> I don't have any specific information about charging time, but I expect it would be fast. It was obviously not all that important, however, as omitting the charger was one of the weight-saving measures adopted for the Mk V. The guns were loaded and cocked on the ground.
> 
> In those pre-electronic days I don't believe there would have been any automatic detection or rectification of firing problems.



Googling “automatic remote cocking mechanism” brings little up re WW2 weapons though Denel seem to have something for 50 caliber guns that are remotely operated from armoured vehicles. I imagine it could be done electromechanicaly fairly easily. For instance if the gun trigger is pressed it also closes a switch to rotate a small electric motor. This motor turns a cam through a clock work mechanism and a clutch. If the cam manages to rotate say 180 degrees it will close a switch that cocks and charges the canon and disposes of the dud or jamed round. If the canon however cycles properly it will momentarily open the clutch through a lever as the bolt or barrel moves.

That what seems a simple automatic jam clearing mechanisms like this didn’t exist suggests a different thought process more along the lines of “we will make a weapon so reliable it won’t need recocking in flight”. Uktimatly that was the revolver canon.

PS, who came up with the idea of resurrecting the Gatling mechanism?


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## jmcalli2 (Nov 13, 2020)

gomwolf said:


> US Ballistic Research Laboratories tested some WW2 fire arms in 1947. Title of the reprot is "Airplane Vulnerability and Overall Armament Effectiveness".
> They tested 50cal, 60cal(US copied MG151/15), 20mm Hispano, 3cm MK108, 37mm M4.
> I am quite sure you will find your own conclusion after read this report.
> 
> Personally I believe bigger HE shell is more effective to aircraft. Cuz it can destroy aircraft's structure itself even if shell didn't hit the vital parts.



I'm leaning towards rate of fire as a more important factor for one reason: how far is it between shells?
Say you have a gun firing 1,200 rnds/minute; that's 20 rounds per second (1,200 rounds per minute divided by 60 seconds per minute equals 20 rounds per second). 
If the muzzle velocity is 2,400 ft/sec, then there are 120 feet between rounds (2,400 feet per second divided by 20 rounds per second equals 120 feet between rounds).

A M61 Vulcan fires ~3,000 rnds/min at ~3,000 ft/sec; there are 60 feet between rounds.

A M2 .50cal fires ~800 rnds/min at 2,700 ft/sec; 202 feet between rounds!

A M4 37mm fired 150 rnds/min at 2,000 ft/sec; 800 feet between rounds!

Makes me wonder how these guys ever put more than one round on any target!


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## tomo pauk (Nov 13, 2020)

jmcalli2 said:


> I'm leaning towards rate of fire as a more important factor for one reason: how far is it between shells?
> Say you have a gun firing 1,200 rnds/minute; that's 20 rounds per second (1,200 rounds per minute divided by 60 seconds per minute equals 20 rounds per second).
> If the muzzle velocity is 2,400 ft/sec, then there are 120 feet between rounds (2,400 feet per second divided by 20 rounds per second equals 120 feet between rounds).
> 
> ...



If the pilot is a good marksman, and/or has excellent sight (late ww2 ones were far better than the ones from 1920s/30s), and/or he is a very good pilot thus can fly very close to the target, he will land burst on it's target. Shells/bullets from the burst will stand a good chance to hit in close proximity.
If nothing of the above is present, his bursts will never land on target, even if he has a 10000 rd/min gun.

(the chaps from Zagreb-Borongaj barracks managed to sever the line attaching to the target drogue and the aircraft, carried the parts of the line as a trophy back to the barracks; gun in question was the powerful 30mm of Czech origin; our crews - from Ljubljana Polje barracks, where I've also served - never managed it)

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## BiffF15 (Nov 13, 2020)

jmcalli2 said:


> I'm leaning towards rate of fire as a more important factor for one reason: how far is it between shells?
> Say you have a gun firing 1,200 rnds/minute; that's 20 rounds per second (1,200 rounds per minute divided by 60 seconds per minute equals 20 rounds per second).
> If the muzzle velocity is 2,400 ft/sec, then there are 120 feet between rounds (2,400 feet per second divided by 20 rounds per second equals 120 feet between rounds).
> 
> ...



jmcalli2,

The M61A1 Vulcan cannon (designed by General Electric - "We bring good things to life") as installed in F15, F16, & F18 fires at a cockpit selectable rate of either 3 or 6k/min. In the Eagle we kept it on 6k. Total rounds count in the light grey Eagle is 940. The lesser planes carried less...

Cheers,
Biff

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## Shortround6 (Nov 13, 2020)

jmcalli2 said:


> I'm leaning towards rate of fire as a more important factor for one reason: how far is it between shells?
> Say you have a gun firing 1,200 rnds/minute; that's 20 rounds per second (1,200 rounds per minute divided by 60 seconds per minute equals 20 rounds per second).
> If the muzzle velocity is 2,400 ft/sec, then there are 120 feet between rounds (2,400 feet per second divided by 20 rounds per second equals 120 feet between rounds).
> 
> ...



I think you are looking at this from the wrong direction. 

If a plane doing 300mph (440fps) flies in front of a gun firing at 20 rps and does so in a 90 degree path to the gun then the gun will put a bullet into the airplane every 22 ft of it's length. 

This is regardless of the speed of the bullet or the distance to the target (for practical purposes). A 600rpm (10 rps) gun gets a hit every 44 ft. 

as the angle changes the bullet holes will get closer together. For instance (If i have done the math right) a plane doing 300mph (440fps) and flying in front of our fixed gun will take a bullet hole evey 11 ft from the 20rps gun and one every 22 ft from the 10rps gun. The plane takes twice as long to get through the 'danger space" due to the long distance flown. Obicouls it will take a very lucky hit to bring down a plane even with multiple guns. However the gun/s are not fixed in space and they are supposed to be tracking the target (changing their angle between shots) 

Both factors are important. High velocity comes into play, not to decrease the distance between bullets but to reduce the time of flight from when the bullet leaves the barrel until it gets to the target (or the area the target is in). The pilot (or gunner) will try to aim/move his gun/s so they are pointed ahead of where the target is at the moment of firing and try to get the bullets into the part of the sky where hi thinks the target plane will be in 1/4 to 1/2 a second (our 300mph plane will move 110-220 ft in that time), The less distance the target moves before the bullets get there the greater the chances for hits. trying to _estimate exact_ course, speed and altitude change (plane goes up or down 10 ft in that fraction of a second the bullets take to get there?)

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## Admiral Beez (Nov 14, 2020)

Greyman said:


> A couple of the heavier British cannon (Vickers 'S', Mollins 'M') are sometimes referred to as 2pdr and 6pdr respectively -- but I think the official designations stuck with metric.


But why define cannons by mass?  I know that’s naval tradition.


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## A.G. Williams (Nov 14, 2020)

Admiral Beez said:


> But why define cannons by mass? I know that’s naval tradition.


Not just naval. During WW2 the British Army had the 2 pdr and 6 pdr tank/anti-tank guns as mentioned, plus the 17 pdr T/AT and the 25 pdr and 60 pdr artillery pieces. 

However, it is true that starting with the introduction of the Hispano, the RAF favoured metric designations in all new aircraft guns, with the exception of the 6 pdr Molins.

I must admit I don't understand the British nomenclature at that time. The army had three light field artillery pieces in service in WW2: the 25 pdr Field Gun (87mm calibre ), 95 mm Infantry Howitzer (94mm), and 3.7 inch Mountain Howitzer (94mm).


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## GregP (Nov 14, 2020)

If you Google "the great fighter gun debate," you can see tehre are several ways to consider guns.
1) For a machine gun, you have the kinetic energy times the firing rate minute. The Soviets divide this by the weight of the gun so they can factor in the gun installation.
2) For a machine gun, you could also evaluate the momentum. p = mv, so bullet mass times muzzle velocity.
3) For a cannon, you have the energy or momentum and then you have to figure in the elxplosive content. Some people take the percent explosive divided by ten, add it to 1 and then add that to the energy or momentum. There are several ways to account for the explosive content.

The point is, there are several ways to evaluate guns.

From what I've read, it takes about 2 - 3 times the number of machine guns hits to knock down a fighter versus 20 mm cannons, but that depends on where the hits are. Either a cannon or a MG round would likely pass through a wing tip without much damage. Either one would cause damage if it hit a wing attach point, but the cannon would do 2 - 4 times the damage.

Once you get to 30 mm cannons, there is no contest. One 30 mm cannon hit will lielly known donw a fighter unless it passes through an area that is just sheet metal with nothing in the middle to set off the round.

All we can say for sure is that there are no fighters around troday without cannons. The Soviet MiG-15 was a VERY hard-hitting airplane. It had two 23-mm cannon and one 37-mm cannon. If you got hit, you were likely going down or, at the least, you were out of the fight.

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## pbehn (Nov 14, 2020)

Admiral Beez said:


> But why define cannons by mass? I know that’s naval tradition.


Why define by diameter, you can get a 0.5" handgun. A diameter and especially a metric measure gives a cloak of exactness, in fact, the diameter of a weapon is no more informative than the weight of the projectile.


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## pbehn (Nov 14, 2020)

GregP said:


> If you Google "the great fighter gun debate," you can see tehre are several ways to consider guns.
> 1) For a machine gun, you have the kinetic energy times the firing rate minute. The Soviets divide this by the weight of the gun so they can factor in the gun installation.
> 2) For a machine gun, you could also evaluate the momentum. p = mv, so bullet mass times muzzle velocity.
> 3) For a cannon, you have the energy or momentum and then you have to figure in the elxplosive content. Some people take the percent explosive divided by ten, add it to 1 and then add that to the energy or momentum. There are several ways to account for the explosive content.
> ...


From the picture of a Spitfire hit by 3 or 4 cannon rounds posted here a few times, the side of the fuselage opposite to where the hits occurred ceased to be a stressed skin structure, not only pierced by many fragments of shrapnel but also blown out like a balloon. The pilot was a very lucky man.


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## swampyankee (Nov 14, 2020)

Admiral Beez said:


> But why define cannons by mass? I know that’s naval tradition.


Until shells became common, it was pretty much universal.


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## pbehn (Nov 14, 2020)

swampyankee said:


> Until shells became common, it was pretty much universal.


The weight (or mass) was pretty much all that mattered.


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## PAT303 (Nov 15, 2020)

pbehn said:


> From the picture of a Spitfire hit by 3 or 4 cannon rounds posted here a few times, the side of the fuselage opposite to where the hits occurred ceased to be a stressed skin structure, not only pierced by many fragments of shrapnel but also blown out like a balloon. The pilot was a very lucky man.



The plane was under full control the whole time and the pilot landed without incident, his only injury was shrapnel in his feet that went under the seat armor. Cannons are far more effective than MG's but only if the ammunition was reliable, the German 20mm ammunition used in the BoB was fitted with a graze fuse that was too sensitive which is the reason the three hits on the Spit detonated on the outer skin.





It's the buckle above the far right hit that ended it's career and caused it to become a workshop donor.

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## msxyz (Dec 26, 2020)

The main deciding factor of cannon vs machine guns is in the 'terminal ballistics'. Since aircrafts are made mostly of aluminum it's safe to assume that any bullet travelling fast enough will pierce through skin, structure elements, tanks, etc and will go on wasting most of its kinetic energy in its arced trajectory down to earth. A hit to the engine block is likely to be more devastating and a 'lucky' hit to a half empty fuel tank full of gasoline vapors can also be devastating (especially if the bullet is a tracer or has a phosphor tip) but that's more a matter or luck. An African hunter caught off guard once killed a charging bull elephant with a .22LR rifle of his wife by hitting the poor animal straight through the eye, but that doesn't make the .22LR an elephant gun!

The reason behind having a volley of 4-8 machine guns firing a stream of light bullets at a high rate was that the bullets would act as a wire saw cutting loose large portions of the skin or even the structural trusses of the airplane. Also, without sophisticate predicting gunsights firing a lot of bullets increased the odds that some would hit a vital part of the plane (engine, pilot, tank): same as the good old days in the age of sails when ships fired round balls, sometimes bouncing on the sea surface, in hope of cutting masts, tearing holes near the waterline, etc...

As planes got sturdier, however, sometimes it would take several hundred bullets to down even a simple fighter plane and, most of the time, it was again the result of a 'lucky' hit to the poor pilot, a vital part of the engine, or the usual tank full of inflammable vapors. Any bullet smaller than 20mm cannot contain a HE package large enough to bring more devastation to the plan than pure kinetic energy was already capable of (Italians and Japanese had HE .50mm rounds that they weren't very effective, being designed mainly to set tanks on fire). With a 20mm you can however pack 8-10 grams of HE or even 17 if you design a thin walled shell like the Germans did. That's enough to make the shell burst into splinters that multiply the effect of the hit. Even a small charge (5-6 gr) is able to break the bullet into a handful of heavy fragments travelling in a cone volume starting from the point of impact. 

In addition to that, a 20mm shell weighting 90-130 grams can also defeat the plane armor something that a .50mm machine gun cannot always reliably do. Keep in mind that most pilots fired their guns only when they were very close to the enemy plane; while a .50mm gun is a formidable killer even at 1+ Km distances and it doesn't suffer from trajectory drops as much as a 20mm shell fired from a oerlikon type gun (600-700m/s max), if your target is less than 300m away, you're not going to use the ballistic advantage of the .50mm boat taile bullet, so it's b better to have a slow moving heavy bullet with possibly a HE content.

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## A.G. Williams (Dec 26, 2020)

msxyz said:


> .50mm


I think you mean ".5 inch" (which is 12.7 mm). There were a few aircraft with 50+ mm guns but they didn't see much use.

Those air forces with both 12.7 mm HMGs and 20 mm cannon generally found the cannon to be about three times as destructive.


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## Glider (Dec 26, 2020)

msxyz said:


> The main deciding factor of cannon vs machine guns is in the 'terminal ballistics'. Since aircrafts are made mostly of aluminum it's safe to assume that any bullet travelling fast enough will pierce through skin, structure elements, tanks, etc and will go on wasting most of its kinetic energy in its arced trajectory down to earth. A hit to the engine block is likely to be more devastating and a 'lucky' hit to a half empty fuel tank full of gasoline vapors can also be devastating (especially if the bullet is a tracer or has a phosphor tip) but that's more a matter or luck. An African hunter caught off guard once killed a charging bull elephant with a .22LR rifle of his wife by hitting the poor animal straight through the eye, but that doesn't make the .22LR an elephant gun!
> 
> The reason behind having a volley of 4-8 machine guns firing a stream of light bullets at a high rate was that the bullets would act as a wire saw cutting loose large portions of the skin or even the structural trusses of the airplane. Also, without sophisticate predicting gunsights firing a lot of bullets increased the odds that some would hit a vital part of the plane (engine, pilot, tank): same as the good old days in the age of sails when ships fired round balls, sometimes bouncing on the sea surface, in hope of cutting masts, tearing holes near the waterline, etc...
> 
> ...



There is a lot of sense in this but there are a couple of points where reflection may help
_Since aircrafts are made mostly of aluminum it's safe to assume that any bullet travelling fast enough will pierce through skin, structure elements, tanks, etc and will go on wasting most of its kinetic energy in its arced trajectory down to earth_. LMG's were not as good at this as you may first think. An LMG round can easily be deflected by an aircraft rib and its ability to penetrate fuel tanks with enough effect to damage the self sealing properties is low.
_Keep in mind that most pilots fired their guns only when they were very close to the enemy plane_ Whilst I agree that they should have done, were told and ordered to. The vast majority of pilots fired at too far a distance.


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## PAT303 (Dec 26, 2020)

Glider said:


> LMG's were not as good at this as you may first think. An LMG round can easily be deflected by an aircraft rib and its ability to penetrate fuel tanks with enough effect to damage the self sealing properties is low.



The RAF chose 8 LMG's because a 2 second burst put 300 projectiles into the enemy aircraft which gave the best chance of incapacitating the pilot, it's the reason why late war MkXIV's still carried the .303. Common myth say's the .303's weren't effective against German aircraft in the BoB because they were fitted with armor, what people fail to realise is the armor was fitted because of the number of pilot injuries and deaths suffered in the Battle of France. There are numerous accounts of planes making it back across the channel filled with dead and dying crew or piloted by a crew member that's not the pilot after being hosed by 8 gunned Spits and Hurri's.


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## Glider (Dec 26, 2020)

PAT303 said:


> The RAF chose 8 LMG's because a 2 second burst put 300 projectiles into the enemy aircraft which gave the best chance of incapacitating the pilot, it's the reason why late war MkXIV's still carried the .303. Common myth say's the .303's weren't effective against German aircraft in the BoB because they were fitted with armor, what people fail to realise is the armor was fitted because of the number of pilot injuries and deaths suffered in the Battle of France. There are numerous accounts of planes making it back across the channel filled with dead and dying crew or piloted by a crew member that's not the pilot after being hosed by 8 gunned Spits and Hurri's.



There is no doubt that before the German aircraft were fitted with armour the .303 was an excellent weapon. However once armour and self sealing fuel tanks were fitted then it wasn't nearly as effective.
Again you are partly right when you say _There are numerous accounts of planes making it back across the channel filled with dead and dying crew or piloted by a crew member that's not the pilot after being hosed by 8 gunned Spits and Hurri's. _I say partly as this did happen but if the 303 had been replaced by a heavier weapon, the German bomber wouldn't have made it back.

Lets take a simplistic view on this. There are a number of examples of German bombers making it back (shot to pieces I agree) after being hit by 200 303 bullets. . A 20mm had half the ROF fire of a 303 and a Hurricane could carry 4 x 20mm instead of 8 x 303. Thus 200 303 hits would equal 50 x 20mm. Show me anything that made it home after being hit by 50 20mm shells.

When you say _it's the reason why late war MkXIV's still carried the .303_. I am afraid that your wrong. Late Spit XIV carrier 2 x 0.5 not 4 x 303

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## Shortround6 (Dec 26, 2020)

msxyz said:


> With a 20mm you can however pack 8-10 grams of HE or even 17 if you design a thin walled shell like the Germans did. That's enough to make the shell burst into splinters that multiply the effect of the hit. Even a small charge (5-6 gr) is able to break the bullet into a handful of heavy fragments travelling in a cone volume starting from the point of impact.


The German thin wall shell depended on blast, It broke up into lots of little fragments and not very many big ones so that the distance from the explosion site tended to be rather important to damage done. The thicker wall shells with less explosive were rather a mixed bag. For best fragmentation (optimum size and number) the explosive used had to be matched to the steel alloy and heat treatment of the shell body. Mis matches would result in everything from clouds of dust to a very few big fragments not traveling very fast. Most shells were somewhere in between but it took quite a while to get rid of both the 'make the shell bodies as cheap as you can" and the "fill them with whatever you have available at the time" mentalities. Some countries had little choice at certain points in the war but there was an awful lot of less than theoretical optimum munitions. 



msxyz said:


> In addition to that, a 20mm shell weighting 90-130 grams can also defeat the plane armor something that a .50mm machine gun cannot always reliably do.



This rather depends on the actual shell design. German thin wall shell didn't penetrate very well. Which is why they used a 115-117 gram shell in mixed belts with the Mine shell (mine shell also didn't adapt to tracer very well). Soviet and Japanese light 20mm AP shells are also going to have problems. A 20mm gun is trying to make a hole almost 2.5 times bigger in area than a 12.7mm projectile. That is a lot of material to remove. The 20mm needs to apply as much or more energy to the area of hole per unit as the 12.7mm will. Low power 20mm shells won't do it. Now throw in that most 20mm guns used different types of shells, the HE shells and the AP shells with much less explosive and the versions with tracer which had even less. 



msxyz said:


> while a .50 *CAL* gun is a formidable killer even at 1+ Km distances and it doesn't suffer from trajectory drops as much as a 20mm shell fired from a oerlikon type gun (600-700m/s max), if your target is less than 300m away, you're not going to use the ballistic advantage of the .50 *CAL *boat taile bullet



It is not the drop that screws things up, it is the lead needed. If your .50 cal needs 1.5 seconds to travel 1000yrds your 300mph target will have moved 660ft. adjust as needed. 
Bullet has not dropped anywhere near 600ft at 1000yrds, and if zeroed for even 250 yds or so in a P-38 it won't drop below the line of sight until 550-600yds. Yes it will be low at 1000yds but the main sources of error will be distance estimation, target speed/direction and amount of lead needed.

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## XBe02Drvr (Dec 26, 2020)

msxyz said:


> (Italians and Japanese had HE .50mm rounds that they weren't very effective,





msxyz said:


> something that a .50mm machine gun cannot always reliably do





msxyz said:


> while a .50mm gun is a formidable killer


I guess so! A 50mm machine gun would be firing a projectile nearly two inches in diameter, and the recoil of that in automatic fire would shake just about any plane to pieces.
You don't suppose msxyz meant .50 CALIBER, do you?
OTOH, an actual .50mm round would be about the size of a needle point.


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## Shortround6 (Dec 26, 2020)




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## XBe02Drvr (Dec 26, 2020)

Shortround6 said:


> View attachment 606448


Quite the proboscis! What is it?


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## Shortround6 (Dec 26, 2020)

One of three Me 262s fitted with a 50mm cannon

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## XBe02Drvr (Dec 26, 2020)

Shortround6 said:


> One of three Me 262s fitted with a 50mm cannon


Awesome! Rate of fire, and how many rounds carried? And what's it's estimated service life? Artillery style full hydraulic recoil mechanism? Must be a heavy S.O.B.


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## Shortround6 (Dec 26, 2020)

MK 214A cannon - Wikipedia


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## PAT303 (Dec 26, 2020)

Glider said:


> Again you are partly right when you say _There are numerous accounts of planes making it back across the channel filled with dead and dying crew or piloted by a crew member that's not the pilot after being hosed by 8 gunned Spits and Hurri's. _I say partly as this did happen but if the 303 had been replaced by a heavier weapon, the German bomber wouldn't have made it back.



No they wouldn't have, the shot gun effect of the eight .303's was an attempt to make up for a lack of shooting ability, that's why bombers flew back to France peppered with holes, the average pilot just aimed at big black blob rapidly filling up their windscreen and let rip, the use of cannons in that situation would just have pilots running out of ammo quicker and hitting nothing.


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## PAT303 (Dec 26, 2020)

Glider said:


> When you say _it's the reason why late war MkXIV's still carried the .303_. I am afraid that your wrong. Late Spit XIV carrier 2 x 0.5 not 4 x 303



No you are wrong, 0.5 cals were only fitted after gyro gunsights became standard and reliable ammunition was developed, until that happened two 
Hispano's with HEI and SAPI and four .303's with AP and Incendiary was the standard fitment.


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## Glider (Dec 26, 2020)

PAT303 said:


> No they wouldn't have, the shot gun effect of the eight .303's was an attempt to make up for a lack of shooting ability, that's why bombers flew back to France peppered with holes, the average pilot just aimed at big black blob rapidly filling up their windscreen and let rip, the use of cannons in that situation would just have pilots running out of ammo quicker and hitting nothing.


The use of 8 x 303 was because the RAF knew that with the much faster aircraft a more powerful 'punch' was needed and they were aware that four x 303 on its own wasn't sufficient. The RAF had decided pre war that the 20mm was the way to go but didn't have a suitable weapon, hence the multiple 303 solution.
I notice that you didn't comment on the example I gave which would have allowed for the same level of marksmanship. Clearly far fewer 20mm hits would have been needed and this would have used less ammunition and been a quicker solution. You also didn't comment on my observation that most pilots of all nations tended to fire at too long a range. It is often said that a pilot holding fire until they were close was the sign of an experienced pilot.


> No you are wrong, 0.5 cals were only fitted after gyro gunsights became standard and reliable ammunition was developed, until that happened two
> Hispano's with HEI and SAPI and four .303's with AP and Incendiary was the standard fitment.


On this we will have to agree to disagree.
A couple of points.
a) The GGS and the Spit XIV were introduced at roughly the same time but one was definitely not dependent on the other. Many Spitfires were built with the E wing yet didn't have the GGS. Plus of course many other aircraft were fitted with the GGS as well
b) To believe that the 0.5 didn't have reliable ammunition until so late in the war flies in the face of all the evidence. The USAAF were of course using the 0.5 for a long time before as were the RAF in the American aircraft used by them.
c) I notice that do agree that the later Spit XIV carried two x 0.5. If the 4 x 303 had been so effective there would be nothing to stop the RAF fitting the GGS and keeping the 4 x 303


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## PAT303 (Dec 27, 2020)

Glider said:


> I notice that you didn't comment on the example I gave which would have allowed for the same level of marksmanship



Dowding himself commented on the lack of marksmanship in the RAF, that's why the official Spitfire and Hurricane gun divergence of 12 feet by 8 feet pattern was called the ''Dowding Spread'', because it gave average pilots a chance to hit something. Fitting cannons to aircraft, and remember cannons at that time such as the Mauser FF/M only had 7 seconds of firing time, had ammunition that didn't work properly and you had to get within 150-200m to have a chance of hitting anything, if you look at it they offered no advantage over MG's at that stage of the war.

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## PAT303 (Dec 27, 2020)

Glider said:


> To believe that the 0.5 didn't have reliable ammunition until so late in the war flies in the face of all the evidence.



The .50 BMG only became reliable as a weapon, both gun and ammunition after 1943, you could almost say 1944, the Americans even reversed engineered a scaled up version of the De Wilde .303 round to get an incendiary in production they were so desperate, the AP ammunition likewise tumbled after striking the target limiting it's penetration, there was lots of issue's with aerial weapons, guns cannons ammunition sighting arrangements and training throughout WW2.


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## PAT303 (Dec 27, 2020)

Glider said:


> c) I notice that do agree that the later Spit XIV carried two x 0.5. If the 4 x 303 had been so effective there would be nothing to stop the RAF fitting the GGS and keeping the 4 x 303



They did, huge numbers of MkXIV's had the 2 Hispano 4 .303 armament, it's a whole other argument as to whether 80 AP/incendiary .303's hitting a FW190 or Me109 are going to have the same effect as 25 .50BMG's.


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## A.G. Williams (Dec 27, 2020)

A few comments:

Cannon shells stopped being purely HE quite early in WW2, when it was realised that fire was the main plane-killer. After that, incendiary material was added to the HE, either mixed in a chemical compound or in a separate capsule. After 1942, the standard RAF load-out for the Hispanos was 50/50 HEI and SAPI. The SAPI consisted of the standard HEI shell stuffed with incendiary material and with a hard steel nose cap instead of a fuze - they ignited on impact. So they held around 11g of incendiary, compared with 0.9g for the .50 API (the standard type of late-war .50 ammo). Incidentally, the actual armour penetration of the .50 API was about the same as the 20mm SAPI (both very good), but the behind-armour effectiveness of the 20mm was an order of magnitude greater.

All this talk about an RAF fighter pouring hundreds of .303 rounds into the bombers needs qualifying, since only a very small percentage of the shots fired actually hit. The Luftwaffe increased the calibre of their late-war cannon from 20mm to 30mm as a result of a simple calculation: it took about 20 hits from 20mm cannon to down a heavy bomber, only about three hits from a 30mm. About 5% of shots fired scored hits, which meant that on average the fighter needed to fire 400 20mm rounds at the target to bring it down - rather more than most German fighters could carry. With 30mm, some 60 rounds needed to be fired, which is much more feasible.

A similar calculation could be done for 20mm cannon vs .50 or .303 MGs, only I don't think that the RAF collected and analysed such data quite as thoroughly as the Luftwaffe. It is worth pointing out, however, that they had .303 and 20mm guns in service together for several years, which gave them a good basis for comparison. Their conclusion was that 4 x 20mm was the optimum fighter armament. Other air forces (e.g. the USSR) also preferred 20mm cannon even though they had a very good 12.7mm HMG.

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## A.G. Williams (Dec 27, 2020)

PAT303 said:


> Common myth say's the .303's weren't effective against German aircraft in the BoB because they were fitted with armor, what people fail to realise is the armor was fitted because of the number of pilot injuries and deaths suffered in the Battle of France.



Yes of course, but what mattered was that armour _was_ added before and during the BoB, resulting in the .303" and 7.9mm MGs becoming less effective.


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## fastmongrel (Dec 27, 2020)

In 1939/40 the Browning .303 had a big advantage over the .50 and 20mm.

IT WORKED

The Hispano 20mm and the.50 BMG didn't work when fitted in a flexible wing. No good if you can pump out 600rpm of shells if the damn thing jams as soon as it gets some G forces. Fill the bomber with holes or not fire more than a couple of rounds I know which the pilots would have chosen.


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## A.G. Williams (Dec 27, 2020)

fastmongrel said:


> In 1939/40 the Browning .303 had a big advantage over the .50 and 20mm.
> 
> IT WORKED
> 
> The Hispano 20mm and the.50 BMG didn't work when fitted in a flexible wing. No good if you can pump out 600rpm of shells if the damn thing jams as soon as it gets some G forces. Fill the bomber with holes or not fire more than a couple of rounds I know which the pilots would have chosen.



Well, if we're just focusing on 1939/40 then I would agree that, with the benefit of hindsight, the Hispano was the wrong choice - simply because it wasn't ready in time to be useful in the BoB. My choice would have been the 20mm Oerlikon FFL - basically like the MG-FF but with a longer barrel and firing long-cased, higher-velocity ammunition. It still only weighed 33 kg so you could have six for the same weight as four Hispanos. And the MV was the same as the .303, so the trajectories would match. The Japanese Navy adopted it as the 20mm Type 99-2 and showed how it could be kept competitive by developing a belt feed, plus increasing the rate of fire from c.500 rpm to 620 and then 720 rpm right at the end of the war.

The Oerlikons were thoroughly developed and renowned for their ruggedness and reliability. They suffered from the same too-fast fuzing problem as other cannon ammo at the time, but that was rapidly solved by the RAF and the Luftwaffe by modifying the fuzes.


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## PAT303 (Dec 27, 2020)

fastmongrel said:


> The Hispano 20mm and the.50 BMG didn't work when fitted in a flexible wing.



When the British tested the .50BMG in the Martlet they jammed immediately, they later found out the Americans test fired them with the planes flying straight and level, in 1940 the .50BMG was worthless.



fastmongrel said:


> In 1939/40 the Browning .303 had a big advantage over the .50 and 20mm.
> 
> IT WORKED


Yep, the squadron that had cannon armed Spitfires in the BoB, I think it was 606 Squadron demanded to be re-equipped with .303 armed fighters because the Hispano's didn't work.


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## PAT303 (Dec 27, 2020)

A.G. Williams said:


> My choice would have been the 20mm Oerlikon FFL - basically like the MG-FF but with a longer barrel and firing long-cased, higher-velocity ammunition. It still only weighed 33 kg



You could only have 2 Oerlikons with 60 rounds and two .303's with 300 rounds in a 1940's Spit, your going to have the same problem as the early 109's and A6M, not enough ammo for your primary weapons.


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## PAT303 (Dec 27, 2020)

A.G. Williams said:


> Well, if we're just focusing on 1939/40



We aren't, it just drifted that way, it took time for the .50BMG and various 20mm's to mature into reliable weapons, until they did the .303 8mm 30/06 guns were the best choice.


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## Greyman (Dec 27, 2020)

A.G. Williams said:


> ... I don't think that the RAF collected and analysed such data quite as thoroughly as the Luftwaffe.



ORS studied this in terms of length/number of bursts required to destroy an enemy aircraft (counting strikes on combat film not being practical). It was based on Spitfire, Typhoon, Tempest and Mustang combats vs. 109s and 190s (sample size vs. other LW aircraft was too small to draw conclusions).

Now, it sounds like a flippant conclusion by a disinterested party -- but it really did come down remarkably close to:
1 x 20-mm Hispano was as lethal as 2 x .5-inch Brownings​1 x .5-inch Browning was as lethal as 2 x .303-inch Brownings​

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## tomo pauk (Dec 27, 2020)

FWIW, German data and calculations about the effectiveness of guns and guns' set-ups. The number of rounds required is, to the best of my knowledge, for a 4-engined bomber. Translation by your truly.

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## A.G. Williams (Dec 27, 2020)

tomo pauk said:


> FWIW, German data and calculations about the effectiveness of guns and guns' set-ups. The number of rounds required is, to the best of my knowledge, for a 4-engined bomber. Translation by your truly.



Very interesting, thanks for posting this. I am slightly confused about the note in brackets underneath the title: I assume that all the ammo consisted of mine shells except for the MG 151/15? It would otherwise be very odd that the MG 151/15 required almost four times as many hits as the MG 151/20 to down the target. It also seems odd that the number of guns assumed for the MG 151/15 is six, compared with only four for the MG 151/20. I don't know of any Luftwaffe planes which carried six MG 151/15!


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## A.G. Williams (Dec 27, 2020)

PAT303 said:


> You could only have 2 Oerlikons with 60 rounds and two .303's with 300 rounds in a 1940's Spit, your going to have the same problem as the early 109's and A6M, not enough ammo for your primary weapons.



The advantage of the trajectory matching is that the MGs could be used to correct the aim with the cannon only joining in when hits were being scored. With two .303s, one would be loaded with the B. Mk IV incendiary tracers (which left a smoke trail) while the other could have B. Mk VI (Dixon "De Wilde") incendiaries which flashed on impact.

Besides, in an alternative universe, if the Oerlikon had been chosen instead of the Hispano, there would have been plenty of time to develop a belt-feed before the war, instead of all of the time wasted negotiating, testing and debugging the Hispano.

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## tomo pauk (Dec 27, 2020)

A.G. Williams said:


> Very interesting, thanks for posting this. I am slightly confused about the note in brackets underneath the title: I assume that all the ammo consisted of mine shells except for the MG 151/15? It would otherwise be very odd that the MG 151/15 required almost four times as many hits as the MG 151/20 to down the target.



Yes, you're right wrt. the ammo type used. A bit clumsy translation on my part.



> It also seems odd that the number of guns assumed for the MG 151/15 is six, compared with only four for the MG 151/20. I don't know of any Luftwaffe planes which carried six MG 151/15!



Table is probably both of theoretic and practical value? In theory, a six 15mm battery could be carried by Fw 190, Ta 152 or many of 2-engined fighters, but for practical & obvious reasons it was never attempted.
Probably the main lesson for the readers of the table was, back in winter of 1944/45, that 15mm is beyond obsolete for the target type Germans were most interested in killing?


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## tomo pauk (Dec 27, 2020)

A.G. Williams said:


> ...
> Besides, in an alternative universe, if the Oerlikon had been chosen instead of the Hispano, there would have been plenty of time to develop a belt-feed before the war, instead of all of the time wasted negotiating, testing and debugging the Hispano.



Bingo.


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## Greyman (Dec 27, 2020)

A.G. Williams said:


> ... all of the time wasted negotiating, testing and debugging the Hispano.



To be fair to the British, I wonder how much development was lost with the fall of France. In 1939 it ruled by the Director of Armament Development that British and French guns were to be completely interchangeable for installation -- so my assumption is that development would be in tandem, and that the French firm would have the stronger grasp on the situation.

Maybe another one of those _'gee 1938 Britain, didn't you know there were going to be Messerschmitt bases in Calais?'_ situations.


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## tomo pauk (Dec 27, 2020)

Far more time was wasted before the fall of France. Oerlikon was selling both actual cannons and licences to countries years before ww2 - both Germany and France were buying, Poland was offering PZL P.24 fighters with Oerlikon cannon.

Germans were already in 1914 at the shores of the Channel, crushing Belgium in process. Anyone want a bet that next time they will not do it, and then some?


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## PAT303 (Dec 27, 2020)

A.G. Williams said:


> The advantage of the trajectory matching is that the MGs could be used to correct the aim with the cannon only joining in when hits were being scored. With two .303s, one would be loaded with the B. Mk IV incendiary tracers (which left a smoke trail) while the other could have B. Mk VI (Dixon "De Wilde") incendiaries which flashed on impact.
> 
> Besides, in an alternative universe, if the Oerlikon had been chosen instead of the Hispano, there would have been plenty of time to develop a belt-feed before the war, instead of all of the time wasted negotiating, testing and debugging the Hispano.



You have made some very good points, not picking the Oerlikon can go up there with not fitting aux fuel tanks to Spitfires as two ''shakes my head'' moments regarding the RAF.


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## yulzari (Dec 28, 2020)

It is interesting to note that the Finns, who had a variety of guns on a variety of fighters, dealt with these issues by concentrating on the quality of the pilots and firing at close distances. Not that they would have been averse to bigger guns on better fighters, if they could get them.

On a different tack. I don't recall the source but I do recall a quote that Commonwealth pilot training concentrated so much on airmanship and so little on marksmanship that it resulted in pilots who could miss the target from closer to the enemy and at better approaches. It probably could be applied equally to most air forces.


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## A.G. Williams (Dec 28, 2020)

PAT303 said:


> You have made some very good points, not picking the Oerlikon can go up there with not fitting aux fuel tanks to Spitfires as two ''shakes my head'' moments regarding the RAF.



For clarification, there were three different sizes of 20mm Oerlikon aircraft guns for sale in the mid-1930s:
1. FF (20 x 72RB ammo, weight 24 kg; RoF 520 rpm, MV 600 m/s)
2. FFL (20 x 102RB ammo, weight 33 kg, RoF 500 rpm, MV 750 m/s)
3. FFS (20 x 110RB ammo, weight 39 kg, Rof 470 rpm, MV 820 m/s). This was a lightweight version of the famous Type SS AA gun extensively used by the RN and USN in WW2.

In my view, the MV of the FF was too low. It's a bit of a toss-up between the FFL and FFS; I prefer the FFL for the RAF because of the trajectory matching with .303 and to keep the size and weight down as much as possible. For the US (and especially the USN) the FFS would make more sense because it used the same ammo as the AA gun, and the velocity was a closer match with the .50 BMG.

In fairness to the RAF, when they made their choice of the Hispano in 1935, the contemporary Oerlikon it was compared with was relatively heavy and slow-firing, as it was the French HS 9 which weighed 48 kg and fired at 400 rpm; the prototype HS 404 weighed 50 kg and fired at 700 rpm (it also had a higher MV at c.880 m/s), so looked much better. Shortly afterwards, Oerlikon completely revamped their cannon range to reduce weight and increase the rate of fire as detailed above; while the HS 404 rate of fire was dropped to 600 rpm in the interest of reliability. So there was suddenly not such a big difference between the performance of the HS 404 and the significantly lighter FFS; and the API blowback mechanism of the Oerlikon had much smoother recoil and did not suffer from the installation problems of the Hispano.

So it could be argued that the RAF was rather unlucky with their timing; they urgently wanted a 20mm cannon and the HS 404 seemed to be the most promising one on the market at that time. A few months later and the Hisso's advantage had virtually disappeared.

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## davparlr (Dec 28, 2020)

BiffF15 said:


> I think there is room here for a few more variables. First, if instead of 6 x .50s one went with 4 but increased the ammo it would give a commensurate increase in trigger time. Second, I think in combat there is a “it depends”. Reliability would be number one, or in other words knowing that when I squeezed the trigger that the guns would work. I would take reliability as my number one choice, then increased rounds count (longer trigger time / Mk14 type gunsight?) until I became a confident shooter, then would switch to heavier caliber.
> 
> Food for thought.
> 
> ...


Interestingly, both the F4F-3 and the P-51B both had four .50s and were replaced by six .50s configuration, F4F-4 and P-51D. One possible reason was reliability. There seemed to be a common complaint about jamming of the .50s. The loss of one or two guns on a four gun set certainly would be more problematic than the loss of one or two guns on a six gun set. The P-51B was certainly a successful aircraft and fought a good portion of the war, I suspect even to the end of the war. The F4F-4 had less ammo available thus shorter firing time.


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## varsity07840 (Dec 28, 2020)

davparlr said:


> Interestingly, both the F4F-3 and the P-51B both had four .50s and were replaced by six .50s configuration, F4F-4 and P-51D. One possible reason was reliability. There seemed to be a common complaint about jamming of the .50s. The loss of one or two guns on a four gun set certainly would be more problematic than the loss of one or two guns on a six gun set. The P-51B was certainly a successful aircraft and fought a good portion of the war, I suspect even to the end of the war. The F4F-4 had less ammo available thus shorter firing time.


The problem with the P-51B/C was that the guns were angled in the bays, causing feeding problems. The six gun F4F-4 was an off spring of a FAA requirement for folding wings and six guns. The six guns with less ammo was almost universally condemned by veteran pilots.


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## varsity07840 (Dec 28, 2020)

PAT303 said:


> When the British tested the .50BMG in the Martlet they jammed immediately, they later found out the Americans test fired them with the planes flying straight and level, in 1940 the .50BMG was worthless.
> 
> 
> Yep, the squadron that had cannon armed Spitfires in the BoB, I think it was 606 Squadron demanded to be re-equipped with .303 armed fighters because the Hispano's didn't work.


Was that the gun or the mounts? Considering the problems with the P-51B/C, I'm thinking it was the mounts.


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## Greyman (Dec 28, 2020)

Both, at that stage. More so the mounts though, by the sounds of it.

Got into it near the start of this thread:
Wildcat during the Battle of Britain


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## A.G. Williams (Dec 29, 2020)

I don't have any data on .50 reliability except for some late-war figures which show that it experienced one stoppage every 4,500 rounds (the Hispano managed 1,500 rounds). 

Looking at the history of the .50 Browning; the original M1921 was completely reworked in the early 1930s and emerged as the M2. So the gun was around for the best part of a decade before the US got involved in the war - which should have been plenty of time to sort any problems. However, the aircraft gun was modified in around 1940 to improve its rate of fire (from c.600 rpm to 800 rpm IIRC) and possibly this increase affected reliability until this was sorted. It generally seems to have been regarded as reliable once combat got going.
.


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## Shortround6 (Dec 29, 2020)

I believe that the M2 aircraft gun had the belt pull (force exerted on the belt by the feed pawls) doubled at some point in 1940 or 41, this may have been in conjunction with the increase in rate of fire done at the same time. There was no change in nomenclature for either change. The increase in belt pull should have solved some (but not all) of the feed problems. 
Guns in the field could be converted with suitable parts, how long that took to accomplish is not reported so far.


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## Greyman (Dec 29, 2020)

I think it's extremely difficult to put exact numbers on overall reliability of weapon X or Y. 

Stoppages rates could vary significantly: 

over time -- eg: VIII Fighter Command Lightnings went from about 1750 rounds (.50-cal) per stoppage at the beginning of 1944 to about 5750 rounds by the middle of the year.
between installations -- eg: VIII FC Mustangs had a stoppage rate of about 750 rounds per -- while the Thunderbolts were about 1750 per (spring 1944)
between units -- I can't find the document anywhere at the moment, but I have an RAF report on fighter operations in Tunisia (I think) that noted the importance of weapon maintenance in this regard, giving figures for the average Hispano stoppage rate and the rate of the worst squadron in this respect. The difference was significant.

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## davparlr (Dec 29, 2020)

A.G. Williams said:


> - which should have been plenty of time to sort any problems.
> .


Pre-war validation of U.S. combat equipment seemed to be lacking, probably due to lack of adequate funding. Most noted was the torpedo fiasco, but there was also issues with the radios, certainly with the Navy, where critical information did not reach the right place at the right time (probably poor procedures aided this problem), in addition to the .50 cals. Of course this happens with even more modern equipment, like the M-16, unfortunately people die when equipment does not work properly. And, it's difficult to test equipment to actual combat levels. Also, even today it seems that too many lessons are learned from dead bodies instead of equipment testing like in the 737Max. Airbus had similar failures only lucked out due to altitude when failures occurred which allowed crew to adapt. Ironically, had an Airbus software operating failure caused a loss of aircraft/people, the 737 fiasco may not occurred.


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## Koopernic (Dec 30, 2020)

A.G. Williams said:


> For clarification, there were three different sizes of 20mm Oerlikon aircraft guns for sale in the mid-1930s:
> 1. FF (20 x 72RB ammo, weight 24 kg; RoF 520 rpm, MV 600 m/s)
> 2. FFL (20 x 102RB ammo, weight 33 kg, RoF 500 rpm, MV 750 m/s)
> 3. FFS (20 x 110RB ammo, weight 39 kg, Rof 470 rpm, MV 820 m/s). This was a lightweight version of the famous Type SS AA gun extensively used by the RN and USN in WW2.
> ...



Is there a figure of merit to measure peak recoil force versus average recoil force. Presumably the heavy recoil of the Hispano due to the mechanism and heavy round required strengthening of the aircraft spars

It also occurs to me that the optimal configuration or armament may have been mixed 20mm ie Hispano V plus MG FFS or FFL in parts of the airframe less suited. Hispano V with MG151/20 might even work. Would a Typhoon have been able to carry 6 MG151/20 or Oerlikon in Lieu of 4 Hispano or a mixture?

Did the Germans ever become serious about the C30/C38 on aircraft? Closest they seem to have gotten was the MG213 which seems to have almost the same parameters.


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## A.G. Williams (Dec 30, 2020)

Koopernic said:


> Is there a figure of merit to measure peak recoil force? Presumably the heavy recoil of the Hispano due to the mechanism and heavy round required strengthening of the aircraft spars



The Hispano was a powerful gun which did not have an integral support (as a motor cannon, the support was supposed to be provided by bolting the gun to the engine). The peak recoil blow was considerable (the massive 57mm Molins aircraft gun carried by the DH Tsetse had a very long recoil movement, and a peak recoil blow similar to the Hispano's). 

The Oerlikons enjoyed the benefit of their Advance Primer Ignition Blowback mechanism, which meant that the gun fired as the bolt was travelling forwards at maximum speed. The initial recoil blow therefore went into stopping the bolt's forward movement, and much of the remainder on pushing it back again, which produced a much smoother curve on the recoil graph with a low peak blow. These were ideal characteristics for aircraft cannon, making mounting the guns much easier.

Mixing different types of cannon in one installation was an unwelcome complication, not just in terms of logistics but also ballistics. The Luftwaffe did field some Fw 190 with MG 151/20 in the wing roots and MG-FF in the outer wings, but I gather that the MG-FFs were often removed.

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## buffnut453 (Dec 30, 2020)

A.G. Williams said:


> It generally seems to have been regarded as reliable once combat got going..



Rather depends on your definition of that timeframe. I'm sure the P-40 pilots in the Philippines, Buffalo pilots in Singapore, F4F pilots thru Q3 1942, and P-51 pilots well into 1943 would have preferred more reliable weapons than they experienced. Pretty much every wing installation of 50cals seems to have been problemmatic for many months after the US entered the war, and in some cases well into 1943. Which timeframe do you consider as when "combat got going"?


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## A.G. Williams (Dec 30, 2020)

buffnut453 said:


> Rather depends on your definition of that timeframe. I'm sure the P-40 pilots in the Philippines, Buffalo pilots in Singapore, F4F pilots thru Q3 1942, and P-51 pilots well into 1943 would have preferred more reliable weapons than they experienced. Pretty much every wing installation of 50cals seems to have been problemmatic for many months after the US entered the war, and in some cases well into 1943. Which timeframe do you consider as when "combat got going"?



Interesting. In the reading that I've done about aircraft guns, I have come across exhaustively detailed accounts of the problems of the Hispano and the continuing efforts to correct them (and also about the 37mm M4 ejection and how that was tackled), but virtually nothing about the Browning, apart from the problem with the canted wing installation which proved unreliable.

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## buffnut453 (Dec 30, 2020)

A.G. Williams said:


> Interesting. In the reading that I've done about aircraft guns, I have come across exhaustively detailed accounts of the problems of the Hispano and the continuing efforts to correct them (and also about the 37mm M4 ejection and how that was tackled), but virtually nothing about the Browning, apart from the problem with the canted wing installation which proved unreliable.



Lundstrom mentions persistent problems with wing 50 cals into Q3 of 1942 in "The First Team". Various books about the defence of the Philippines mention issues with wing 50cals in P-40s. The Buffalo's issues are well-known (but tend to be highlighted, whereas the issues with other aircraft tend to be ignored). 

Jamming belt feeds and inadequate gun solenoids appear to be the most common issues, but it's surprising (to me, at least) that they persisted so long. I find it truly odd that the P-51, which was a relative late-comer to the party, still had problems with 50cal wing installations.


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## PAT303 (Dec 30, 2020)

Quite a few RAAF pilots complained about the .50's in the P40's we received because of jamming, and a lot more about the HIspano's because of out of spec ammo.


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## A.G. Williams (Dec 30, 2020)

buffnut453 said:


> Lundstrom mentions persistent problems with wing 50 cals into Q3 of 1942 in "The First Team". Various books about the defence of the Philippines mention issues with wing 50cals in P-40s. The Buffalo's issues are well-known (but tend to be highlighted, whereas the issues with other aircraft tend to be ignored).
> 
> Jamming belt feeds and inadequate gun solenoids appear to be the most common issues, but it's surprising (to me, at least) that they persisted so long. I find it truly odd that the P-51, which was a relative late-comer to the party, still had problems with 50cal wing installations.



Thanks for that. I suppose one factor was that aircraft guns tended to be tuned to give the highest performance for the least weight, and were often operating on the ragged edge of reliability. The Soviets, for instance, worked out that the life of an aircraft gun in combat was very short, so they built them to last only just long enough.


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## A.G. Williams (Dec 30, 2020)

PAT303 said:


> Quite a few RAAF pilots complained about the .50's in the P40's we received because of jamming, and a lot more about the HIspano's because of out of spec ammo.


In what respect was the ammo out of spec? The RAF corrected the main problem of light firing pin strikes, by shortening the chamber. See: Modifications and Attempts at Standardization


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## tomo pauk (Dec 30, 2020)

A.G. Williams said:


> Thanks for that. I suppose one factor was that aircraft guns tended to be tuned to give the highest performance for the least weight, and were often operating on the ragged edge of reliability. The Soviets, for instance, worked out that the life of an aircraft gun in combat was very short, so they built them to last only just long enough.



Do we have some quantification about the number of bullets fired before the guns were rendered useless? Eg. when Soviets tested the Beresins' HMG, the guns were good for 10000-12000 rounds fired.


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## PAT303 (Dec 30, 2020)

A.G. Williams said:


> In what respect was the ammo out of spec? The RAF corrected the main problem of light firing pin strikes, by shortening the chamber. See: Modifications and Attempts at Standardization



The Oz made 20mm ammo was terrible, a new factory was set up at St Mary's on the outskirts of Sydney and it was way out of spec.


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## Greyman (Dec 30, 2020)

A.G. Williams said:


> Thanks for that. I suppose one factor was that aircraft guns tended to be tuned to give the highest performance for the least weight, and were often operating on the ragged edge of reliability. The Soviets, for instance, worked out that the life of an aircraft gun in combat was very short, so they built them to last only just long enough.



From the Air Historical Branch re: Hispano V -- 

_It was decided to take this opportunity to redesign the gun completely and to incorporate into the new gun; the short barrel, increased rate of fire and light weight. One of the first questions to decide was the acceptable life of the new gun. Before the war a life of at least 20,000 rounds was expected for rifle calibre guns, and the acceptable life of the Hispano 20-mm gun had been fixed at 10,000 rounds. It was apparent that under active service conditions few aircraft survived to give 10,000 rounds and an investigation was made to determine the actual life of guns under war service. The results were surprising: it appeared that very few guns ever reached 1,000 rounds, and the majority only fired a few hundred before the aircraft crashed or was lost in action. There was obviously no point in aiming at a 10,000 rounds life, and the Air Staff were asked to accept one of 1,500 rounds. _​​_... _​​_Subsequent experience with production guns in service showed that the average life of the smaller components was 2,500 to 3,000 rounds, while the barrel was good for at least 5,000 rounds. _​

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## A.G. Williams (Dec 30, 2020)

PAT303 said:


> The Oz made 20mm ammo was terrible, a new factory was set up at St Mary's on the outskirts of Sydney and it was way out of spec.


Right, thanks.


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## A.G. Williams (Dec 30, 2020)

tomo pauk said:


> Do we have some quantification about the number of bullets fired before the guns were rendered useless? Eg. when Soviets tested the Beresins' HMG, the guns were good for 10000-12000 rounds fired.


I have a few bits and pieces of information concerning Soviet aircraft guns. 

The NS-23 (right at the end of WW2) lasted for 4,000 rounds free, or 3,000 synchronised (more little pieces to go wrong)
The AM-23 (1950s) managed 6,000 rounds
The NR-30 (1950s) 2,000 rounds initially, later 3,000 rounds
The R-23 (1960s) 3,000 rounds
The GSh-23 (1960s) 4,000 rounds (after modification to enhance life)
The GSh-30 (1970s) 4,000 rounds
The GSh-301 (current gun in Su-27 and MiG-29 families): 2,000 rounds (1,000 rounds for the barrel).

For comparison, the US M61A1: gun life 90,000 rounds, barrels 15,000, certain other parts 30,000.

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## Clayton Magnet (Dec 30, 2020)

A.G. Williams said:


> The GSh-301 (current gun in Su-27 and MiG-29 families): 2,000 rounds (1,000 rounds for the barrel).
> 
> For comparison, the US M61A1: gun life 90,000 rounds, barrels 15,000, certain other parts 30,000.


The GSh-30-1 is also remarkably light and compact, with a fantastic rate of fire for a 30mm non-revolving cannon

I would be curious to see any information regarding the reliability of the 20mm cannon version of the Beresin. The B20 checks a lot of boxes for a fighter weapon, light weight and hard hitting


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## tomo pauk (Dec 30, 2020)

A.G. Williams said:


> I have a few bits and pieces of information concerning Soviet aircraft guns.
> 
> The NS-23 (right at the end of WW2) lasted for 4,000 rounds free, or 3,000 synchronised (more little pieces to go wrong)
> The AM-23 (1950s) managed 6,000 rounds
> ...



Thank you.
Do you have anything on the ww2 era guns.


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## A.G. Williams (Dec 30, 2020)

tomo pauk said:


> Thank you.
> Do you have anything on the ww2 era guns.


Sorry, I don't.

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## A.G. Williams (Dec 30, 2020)

Clayton Magnet said:


> The GSh-30-1 is also remarkably light and compact, with a fantastic rate of fire for a 30mm non-revolving cannon



Yes, it is an outstanding design. It fires ammo with the same power as the 30mm MK 103, but at four times the RoF while weighing only one-third (about the same as an MG 151/20) - in other words, it is 12x better in hitting power per kg. PS: it looks as if it could fit in a Bf 109 engine mounting - that would have changed the terms of air warfare!



> I would be curious to see any information regarding the reliability of the 20mm cannon version of the Beresin. The B20 checks a lot of boxes for a fighter weapon, light weight and hard hitting



The Beresin was another outstanding design, matching the performance of the ShVAK at little more than half the weight and was also more compact, yet was stated to be "more reliable". It is a mystery why this was not adopted much earlier than October 1944 as the adaptation to fire 20mm rather than 12.7mm ammo was quite straightforward.

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## OldParts (Dec 31, 2020)

Williams' books are excellent or go to his excellent online resource which he linked above. As others have pointed out not all weapons of the same caliber (diameter) are the same. An example that is familiar to most folks is the 38 special and the 357 magnum. They have the same bore and you can fire 38s in a 357 but you can fire a 357 in a 38 because the cartridge of the 357 is longer. According to the late Jeff Cooper, the case of the 357 was lengthened to prevent people firing the 357 MAGNUM in a 38 which was not built to stand the increased chamber pressure. I once fired about 100 rounds of 38 and 100 rounds of 357 through a light weight (J frame) 3 inch S&W. The 38 and the 357 are the same caliber but the muzzle velocity of the 357 is probably about 40 percent higher than the 38 (depends on the brand, bullet weight, and barrel length). The pistol had stock wooden grips and the web of my hand was bleeding after firing the 357 rounds. Until reading Williams, I had no idea of how large the differences were in the same caliber of automatic cannon and HMG ammunition. Another factor is the type of projectile used (ball (solid), HE, or incendiary, or HEI. What the Browning 50 had going for it was high reliability and projectile that was not so dependent upon an explosion to do a lot of damage. The HS 20 also used a heavy projectile. But many of the German (and Japanese) cannon used thin skinned shells with low muzzle velocities.


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## strider190 (Dec 31, 2020)

grampi said:


> If you were a fighter pilot in WWII, would you rather have the high rate of fire of the 50 cal, or the hitting power of the 20mm? I personally feel the 50 cal was plenty hard hitting enough to take out ANY aircraft, and its high rate of fire made it even more effective...the slow rate of fire for the 20mm meant you had to be a much better marksman...


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## strider190 (Dec 31, 2020)

grampi said:


> If you were a fighter pilot in WWII, would you rather have the high rate of fire of the 50 cal, or the hitting power of the 20mm? I personally feel the 50 cal was plenty hard hitting enough to take out ANY aircraft, and its high rate of fire made it even more effective...the slow rate of fire for the 20mm meant you had to be a much better marksman...



I'd take a 20mm over a .50 cal anytime. Most WW2 fighter types would have agreed. Explosive! No contest.


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## Timppa (Jan 1, 2021)

A.G. Williams said:


> The Beresin was another outstanding design, matching the performance of the ShVAK at little more than half the weight and was also more compact, yet was stated to be "more reliable". It is a mystery why this was not adopted much earlier than October 1944 as the adaptation to fire 20mm rather than 12.7mm ammo was quite straightforward.



I quote Milos Vestsik's book ("Lavockin La-7"):
"The reliability of the cannon was also never to reach the required level, this is documented by the tests carried out with La-7 aircraft, at the NII VVS from September 10 to October 1945. Of the three aircraft in test, none were to attain the expected service life of 5,000 rounds fired (the first test fired 3,275 times, the second 3,222 times, the third 3,155 times)."

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## A.G. Williams (Jan 1, 2021)

Timppa said:


> I quote Milos Vestsik's book ("Lavockin La-7"):
> "The reliability of the cannon was also never to reach the required level, this is documented by the tests carried out with La-7 aircraft, at the NII VVS from September 10 to October 1945. Of the three aircraft in test, none were to attain the expected service life of 5,000 rounds fired (the first test fired 3,275 times, the second 3,222 times, the third 3,155 times)."


Well, my source only said that the Beresin was "more reliable" than the ShVAK. 

I think that the La-7 tests showed astonishing consistency, and the results were almost certainly good enough for combat purposes.

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## Schweik (Jan 1, 2021)

Snowygrouch said:


> This may help. From USAAF microfilm report.
> 
> View attachment 600945
> 
> View attachment 600946



Wow that is one hell of a cool post right there...


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## jmcalli2 (Jan 2, 2021)

Snowygrouch said:


> This may help. From USAAF microfilm report.
> 
> View attachment 600945
> 
> View attachment 600946




Some interesting comparisons here:

The WWII Fighter Gun Debate: The Fighters


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## Thumpalumpacus (Mar 12, 2021)

Shortround6 said:


> View attachment 601455
> 
> 
> Yes the Hispano's were big.
> Hispano's were a hybrid gun. They used a combination of gas and recoil. The shorter lighter barrel helped with the increase in the rate of fire.



Must be a Californian, he's texting even on the flight line.


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## Koopernic (Mar 12, 2021)

A.G. Williams said:


> I have a few bits and pieces of information concerning Soviet aircraft guns.
> 
> The NS-23 (right at the end of WW2) lasted for 4,000 rounds free, or 3,000 synchronised (more little pieces to go wrong)
> The AM-23 (1950s) managed 6,000 rounds
> ...



What kind of stoppage rates and barrel life do modern guns achieve?


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## Greyman (Mar 13, 2021)

Greyman said:


> I can't find the document anywhere at the moment, but I have an RAF report on fighter operations in Tunisia (I think) that noted the importance of weapon maintenance in this regard, giving figures for the average Hispano stoppage rate and the rate of the worst squadron in this respect. The difference was significant.



Found it (report from an Ordnance Board Mission to North Africa and Malta).

_20 m.m. Hispano Gun Mks. I and II and U.S. M2._
_The performance of this gun is generally satisfactory, but it is stressed that this is only after personnel have become thoroughly versed in the meticulous maintenance necessary under active service condition ... the stoppage rate varies from one in 350 rounds to one in 2000 rounds in different squadrons._


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## A.G. Williams (Mar 13, 2021)

Greyman said:


> Found it (report from an Ordnance Board Mission to North Africa and Malta).
> 
> _20 m.m. Hispano Gun Mks. I and II and U.S. M2._
> _The performance of this gun is generally satisfactory, but it is stressed that this is only after personnel have become thoroughly versed in the meticulous maintenance necessary under active service condition ... the stoppage rate varies from one in 350 rounds to one in 2000 rounds in different squadrons._



US figures I have seen (France, 1944) show one stoppage for every 1,500 rounds with the Hispano, one for every 4,500 rounds for the .50 M2.


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## MIflyer (Mar 13, 2021)

Well, remember that the .50 had Armor Piercing Incendiary ammo by 1944 and that really improved its already impressive lethality. Reports from the Pacific reveal that Hellcats were shooting down Vals and such with one carefully aimed round.

And when the RAF realized they would have no choice but to use Spitfires as fighter bombers after the invasion of Normandy they pushed to remove the four .303 guns and replace them with twin .50 cal as soon as possible.


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## Shortround6 (Mar 13, 2021)

Please remember that there are 3 different metrics here, at least. 

Stoppages per XXX number of rounds, this can be a simple jam, round got a bit cross wise, or it can be a broken part. might be a dud round but those might be filtered out (or not, depending on source or country) 

Broken parts were sometimes listed separately. as in broken parts per XXXX rounds fired. Broken part will usually result in a stoppage. 

The you have barrel life and gun life. 
Barrel life is how many rounds you can fire through a barrel before enough rifling gets worn/burned away to affect accuracy and velocity to a certain limit. Perhaps also a variable between nations? 
Gun life is when major components, like receiver and bolt are so worn than it is no longer worthwhile to put in new parts or installing new parts (like a new bolt) will not bring the gun back to factory tolerances. 

The Browning M2 and the Hispano could often be rebuilt/overhauled several times before the receiver was stretched/worn enough that installing new parts would fail to bring it back to operational status.

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## A.G. Williams (Mar 14, 2021)

Shortround6 said:


> Barrel life is how many rounds you can fire through a barrel before enough rifling gets worn/burned away to affect accuracy and velocity to a certain limit. Perhaps also a variable between nations?



There's another aspect to this affecting the barrel life of aircraft guns: the length of the burst fired. A barrel will last far longer if the gun is fired in short bursts, preferably with a cooling-off period between bursts.

I can't vouch for the accuracy of this, but I was once told that if a plane armed with a 27mm Mauser BK 27 revolver cannon fired off all 150 rounds (normal ammo load) in one burst at 1,700 rpm, the barrel would need to be replaced.

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## Shortround6 (Mar 14, 2021)

You are quite right.
US manuals for the .50 go into some detail about burst length and cooling times. Like initial burst can be 75 rounds and following bursts are more like 25 rounds (?) with a certain number of seconds between bursts, obliviously impractical if not impossible in air to air combat. 

For ground guns Melvin Johnson described destroying a BAR in under 800 rounds. Gun was fastened down and trigger fasten back with magazines changed as fast as possible. Wooden fore end started smoking in under 400 rounds, then bust into flames and gun stopped firing when mainspring lost it's temper and failed to return the bolt forward. Of course he was trying to sell his LMG at the time 

Chrome plating barrels could give them much longer life.

But I am just pointing out that these are all different measures and often one measure has nothing to do with another. The Vickers ground gun being a great example, the gun itself lasting for hundreds of thousands of rounds, the barrels lasting for about 10,000rounds (assuming water jacket is kept filled) but the gunners manual detailing 27 different ways it could jam.


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## Clayton Magnet (Mar 16, 2021)

MIflyer said:


> And when the RAF realized they would have no choice but to use Spitfires as fighter bombers after the invasion of Normandy they pushed to remove the four .303 guns and replace them with twin .50 cal as soon as possible.



My understanding was that the "E" wing Spitfires with 2x 20mm and 2x 50 Cal were fielded because the similar trajectories between the projectiles were a better match for the new gyro gunsights, not for any ground attack purpose.

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## MIflyer (Mar 16, 2021)

Clayton Magnet said:


> My understanding was that the "E" wing Spitfires with 2x 20mm and 2x 50 Cal were fielded because the similar trajectories between the projectiles were a better match for the new gyro gunsights, not for any ground attack purpose.



According to an article in Flight Journal on the Spitfire fighter bomber, the push for the .50 cal was based on the ground attack mission. See attached with mention of 2 TAF..

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## pbehn (Mar 16, 2021)

MIflyer said:


> According to an article in Flight Journal on the Spitfire fighter bomber, the push for the .50 cal was based on the ground attack mission. See attached with mention of 2 TAF..
> 
> View attachment 616258
> View attachment 616259


That is basically what this page says too. spitfiresite.com/2010/04/sorting-out-the-e-american-armament-for-the-spitfire-mk-ixxvi.html There were other issues too, By 1944 there were US 0.5" Mgs all over UK and it was more effective in ground attack. I also seem to remember that putting the 0.5 on the inside allowed a longer firing time than the .303s on the outside, the page also mentions the need on some spitfires for more space for oxygen. The comment by Edgar Brooks is also informative.

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## Glider (Mar 16, 2021)

One additional factor for the replacement of the 303 with the 0.5 was that the space saved. It allowed certain items of equipment to be placed where the 303 had been installed. These items allowed the rear internal fuel tank to be fitted increasing the range of the Spitfire.
If the 0.303 had been retained they would have had to redesign the rear tank. The additional oxygen tank was needed because of the extra range of the Spit with the rear tank.

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## Greyman (Mar 16, 2021)

MIflyer said:


> According to an article in Flight Journal on the Spitfire fighter bomber, the push for the .50 cal was based on the ground attack mission.



This goes against what was being said in the discussion between the big-wigs. What I've seen of it, anyway.

One of the arguments in keeping the .303 was the fact that it was better for ground attack -- throwing about three times as many bullets in the air (or at the ground, in this case).


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## Shortround6 (Mar 16, 2021)

Greyman said:


> This goes against what was being said in the discussion between the big-wigs. What I've seen of it, anyway.
> 
> One of the arguments in keeping the .303 was the fact that it was better for ground attack -- throwing about three times as many bullets in the air (or at the ground, in this case).



This rather depends on the intended target/s. Shooting up railroad steam engines and railroad cars might require the .50 cal bullets. Shooting up marching/running soldiers, normal trucks, wagons, etc can be done by either one pretty well, more bullets being an asset. 
The .50 will shoot through more timber, light masonry, dirt/sand and such.

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## Greyman (Mar 17, 2021)

From their writing the secondary armament (MGs) were more for things like radiators, men and horses.

The Hispanos handled the heavier stuff.


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## Darthtabby (Sep 13, 2021)

Snowygrouch said:


> This may help. From USAAF microfilm report.
> 
> View attachment 600945
> 
> View attachment 600946



Hope you don't mind me reaching this far back, but I'm kind of curious what the scale at the bottom of the second image refers to. Weight of metal? The results of some sort of special formula cooking up for measuring destructive power?


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## Snowygrouch (Sep 13, 2021)

Darthtabby said:


> Hope you don't mind me reaching this far back, but I'm kind of curious what the scale at the bottom of the second image refers to. Weight of metal? The results of some sort of special formula cooking up for measuring destructive power?

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## Darthtabby (Sep 20, 2021)

Snowygrouch said:


> View attachment 641414



Belated thanks, 

 Snowygrouch
.

Has anyone here actually read the oft mentioned USN evaluation that rated 20mm three time as effective as .50? I'm kind of curious about it since it appears to evaluate the 20mm's advantage as much more significant then the RAF Operational Research Greyman mentioned, and the second of Snowygrouch's graphs also seems to suggest a less significant difference (though its comparing to planes armed with German cannons rather then the 20mm Hispano).


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## fastmongrel (Sep 20, 2021)

Could be the USN report was talking about the greater HEI content which iirc was roughly three times greater than a .50 BMG round.


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## A.G. Williams (Sep 20, 2021)

fastmongrel said:


> Could be the USN report was talking about the greater HEI content which iirc was roughly three times greater than a .50 BMG round.


The US never fielded any explosive .50 bullets as far as I'm aware (although they did a lot of experimental work on them). By 1944, the standard .50 aircraft loading was the M8 API, which had only about one-tenth of the incendiary content of the 20mm Hispano SAPI (which matched its penetration).


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## pbehn (Sep 20, 2021)

Shortround6 said:


> This rather depends on the intended target/s. Shooting up railroad steam engines and railroad cars might require the .50 cal bullets. Shooting up marching/running soldiers, normal trucks, wagons, etc can be done by either one pretty well, more bullets being an asset.
> The .50 will shoot through more timber, light masonry, dirt/sand and such.


The V1 was very difficult to take down with MGs, just because of its shape and construction.


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## Greyman (Sep 20, 2021)

Darthtabby said:


> I'm kind of curious about it since it appears to evaluate the 20mm's advantage as much more significant then the RAF Operational Research Greyman mentioned



The ORS observation was based on German single-seat fighters only. My guess is that if the scope is expanded to twin and four-engine aircraft -- the disparities would grow.


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## MIflyer (Sep 26, 2021)

Anybody look at this video that addresses that question: 



pbehn said:


> The V1 was very difficult to take down with MGs, just because of its shape and construction.


And because it tended to BLOW UP with such force it could shoot down the interceptor. One problem with intercepting the V-1 at night was that its blowtorch was easy to see but very hard to estimate rnage on. The RAF experimented with using tail warning radars - such as "Monica" or APS-13 - to tell the range to the V-1

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## pbehn (Sep 26, 2021)

MIflyer said:


> Anybody look at this video that addresses that question:
> 
> 
> And because it tended to BLOW UP with such force it could shoot down the interceptor. One problem with intercepting the V-1 at night was that its blowtorch was easy to see but very hard to estimate rnage on. The RAF experimented with using tail warning radars - such as "Monica" or APS-13 - to tell the range to the V-1



If you hit the warhead it would explode for MGs and cannon. The V1 was faster in level flight than almost all interceptors so there wasnt much time to hit coming out of a dive. From behind the kill areas were very small and MG bullets tended to bounce away from the V1 fuselage surface.


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## MIflyer (Sep 26, 2021)

The V-1 airframe was steel and was pretty tough.

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