20mm cannon, best, worst, specs, comparison to LMG, HMG etc.

A 'new' thought, if .50 cal was so substantially less than the 20mm why did the russians use 1x 20mm and 1x.50cal in most their aircraft? (someone else can do the count) Why did most of the 20mm spit have 2x20mm and 2x.50 cal? if the .50 cal was not usefull then would have saved the weight and run 1 or 20mm.
Any argument made for the 20mm being drastically different than .50 has to come to grips with thee independent decisions. My own theory is besides having the .50 cal on hand, the 20mm would create damage in soft parts and the .50 damage the hard parts.

Actually it is borne out by combat. The IJAF believed that 4 x HMG was sufficient until they went up against heavy bombers and then they switched to 20mm as fast as they could. The Japanese HMG was a copy of the USAAF 0.5

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The Jap copy was low rate, lower MV and far less effective than the M2, but so was their 20mm as compared to contemporaries. IMHO this gets real difficult since the japs were much more resource limited. If you look at the planes and armament planned near the end of the war, they were pushing 30mm as their choice. There 20mm setup was to heavy and not effective enough. But this really is whole new discussion as the Japanese experience.

One jam per 1500 rounds would make the 20 mm Hispano MORE reliable than the .50 Browning - depending on who built it. One jam per 750 rounds would make it slightly better than half as reliable.

Over the first 8 months of 1944, the USAAF 8th AF found that the M2 Browning averaged 1 stoppage per 1440 rounds. The 20 mm AN/M2 averaged 1 stoppage per 505 rounds, making the .50 cal almost three times as reliable in US service.

The US Bureau of Ordnance found a stoppage rate in Africa of about 1 stoppage per 1300 rounds.

In comparison, the RAF found between D-Day and the end of the war that their Hispanos averaged 1 stoppage per 1560 rounds. Their M2s jammed about 1 per 2,400 rounds.

The main problem with the Hispano was sensitivity to cold temperatures (which caused jamming in the P-38 in the ETO and also Spitfires over Darwin), a sensitivity to dust (which affected Spitfires and Hurricanes in the MTO and also Spitfires over Darwin) and some sub-standard manufacturing in the feed mechanism and belts (responsible for more than 50% of jams). Once the gun heating problem was sorted in 1942, the RAF reported reliability was more than adequate, with one stoppage recorded per 1600 rounds. Given that the gun life was only about 2,000 rounds, this was seen as sufficient.

If the US hadn't buggered up their re-design, the 20 mm would have been comparably reliable to the .50 cal, at least if maintained properly.

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Thank you so the 200mm was less reliable in combat.

zjtins said:

So do not ask me for a source since you cannot share yours, if you actually have any...

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After the SB2C all USN aircraft that entered service had 20mm. The F6F5 entered service before the SB2C-4. The last corsairs entered service after the SB-2C-4 and had 4 x 20mm.

Exactly they were not reliable.

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As per your quote Those installed on the SB2C were particularly notorious for jams, although the problems were largely worked out in the SB2C-4 and may have been due as much to poor maintenance as anything else in the earlier SB2Cs.
The early ones were unreliable but these were largely resolved with the SB2C-4 why do you ignore the second part of your own quote?

Re your comment on the drum feed. Apart from the very first Spit 1B issued during the BOB the reliability problems of the Spit were resolved, both on the drum fed versions and the belt fed versions. Where is your source for this misinformation

Re your Thank you so the 200mm was less reliable in combat Less reliable doesn't make it unreliable. If the life of the gun is 2000 round and the reliability is one jam per 1,600 rounds that make it a very reliable gun.

If it were reliable it never would have had a problem in the first place.

zjtins said:

Back to one plane again, what about the Spit, MGFF on German ....all drum all problematic.

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Again the misinformations about the MG FF. Business as usual?
Of course, the information about the rate of fire for pre1941 M2 .20 cal is omitted (=600 rpm, rather than 800 rpm for the guns produced in 1941 and after that), as is the lack of the advanced ammo (using the copy of Soviet 12.7mm projectile, available from 1943).

A 'new' thought, if .50 cal was so substantially less than the 20mm why did the russians use 1x 20mm and 1x.50cal in most their aircraft? (someone else can do the count)

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That one is easy - the Soviet HMG is, as most HMGs, far smaller than their 20mm (until the B-20 was introduced). So, in the place of synchronized HMG, in Yaks, there was no way the 20 mm would fit. Of course, once the B-20 was introduced, the diminutive Yak-3 can carry 3 cannons, and so could another modestly-sized fighter, the La-7. The La-5 was outfitted with 2 x 20mm from day one, they did not bothered with MGs too much.
But I'm sure that you know this.

Why did most of the 20mm spit have 2x20mm and 2x.50 cal?

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Now this is interesting. Where that information can be confirmed, since it's as far from the truth as possible.

if the .50 cal was not usefull then would have saved the weight and run 1 or 20mm.

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You do know that 2 x .50 cals were introduced in exchange for 4 x .303s?

Any argument made for the 20mm being drastically different than .50 has to come to grips with thee independent decisions. My own theory is besides having the .50 cal on hand, the 20mm would create damage in soft parts and the .50 damage the hard parts.

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We all have theories. Much of them can be either confirmed or denied by data from credible sources.

The 0.5 was useful. The issue isn't and never has been is the 0.5 not useful, its, is it as effective as the 20mm and the reply is no it isn't.
On the SPitfire the other issue was, is the 303 useful and it wasn't, I read once someone described them as door knockers as all they did was let the Germans know you were there (wish I could find that quote). The 0.5 was a lot better than the 303 and was effective so they installed it instead of the 303.

Why didn't they install 4 x 20mm as standard? Because of the impact on the roll rate which was an area the Spit wasn't so good as compared to the Fw 190 which was a frequent foe, and the climb which was a strength of the Spitfire. When the Spit wing was redesigned for the mk 20 this was catered for and the normal guns were 4 x 20.

zjtins said:

You apparently do not understand damage physics. There is simply is no way to predict or compare prediction for mechanical vs chemical damage, they use different physics.

A .50 cal bullet going through Al skin leaves .50 cal hole, the explosive creates over pressure. The overpressure if constrained (as in a time delay and is inside the plane) expand until a opening is found a one is created at the weakest points.
OTOH a 20mm impact and detonation on the surface of hard object (engine) only has overpressure (generally at point of impact) to damage the hard object. Cast iron and steel can take alot of overpressure. But SAPI .50 round breaks the brittle engine metal. Cracks propagate especially under load. They also can a did pierce the armor plate and other hard objects. The 20mm did not generally go through Armor plate. (Read Bobs book he took several 20mm hits in the armor in his P-47).

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This is so wrong its almost a new level and I would love to see any evidence to prove this and prove me wrong but admit to not holding my breath

The standard laod from 1942 on was 50% HE and 50% API. The 20mm penetrated as much armour as the 0.5in and had the explosive content that the 0.5 so lacked. The Ball was being replaced in 1942 and I submit my evidence

Oh Man, another load of crap.

original quote "If you think that a single 46 gram .50 bullet will wreck and engine when a 128 gram AP 20mm round going about the same speed won't then I guess the laws of physics have been repealed."

Zjtis reply" You apparently do not understand damage physics. There is simply is no way to predict or compare prediction for mechanical vs chemical damage, they use different physics."

What part of 46 gram .50 bullet and 128 gram AP 20mm round didn't you understand? The 20mm AP round has little or no explosive and is depending on the same type of energy as the .50 cal bullet to do damage.

Zjtis "My own theory is besides having the .50 cal on hand, the 20mm would create damage in soft parts and the .50 damage the hard parts."

see above. British SAPI would penetrate as much armor as the .50 cal AP so it should certainly damage any hard parts of the aircraft as it was making a bigger hole and hitting with 3 times the energy before yo take the chemical energy into account. Pure 20mm Hispano AP would penetrate even more "hard parts". Until very late 1943 or early 1944 the US was using mixed belts on the .50 cal guns. Mixed AP and incendiary with tracers according to preference. The .50 cal incendiary ( pre M8 ) isn't going to be any better than the 20mm Hispano, if as good, on "hard parts"

You have been told before WHY the Russians used one 20mm cannon and one 12.7 mm MG. either refute it or leave it alone.

Zjtis "The Jap copy was low rate, lower MV and far less effective than the M2, but so was their 20mm as compared to contemporaries."

The Jap copy had a higher rate of fire than the M2, at least on the early guns before quality (raw materials) fell. it also weighed about 75% as much as the M2. the ammo was smaller and lighter. it weighed about 73% asmuch as th aAmerican .50 cal per round. FOr the weight of TWO JAPANESE 12.7mm machine guns and 500 rounds of ammo (not including links, mounts, ammo boxes and chutes) you can get TWO M2 Brownings with 240 rounds, 120 rounds per gun. Or ONE M2 Browning with 500 rounds of ammo.

WHICH JAPANESE 20mm gun? they used 4 different guns and 4 different cartridges. The more common Japanese Army 20mm, the HO-5 was about 25% heavier than the M2 Browning and fired just about as fast (700-850 rpm). MV was lower but the AP projectile weighed 112 grams and the HE weighed 79 grams.

Glider said:

This is so wrong its almost a new level and I would love to see any evidence to prove this and prove me wrong but admit to not holding my breath

The standard laod from 1942 on was 50% HE and 50% API. The 20mm penetrated as much armour as the 0.5in and had the explosive content that the 0.5 so lacked. The Ball was being replaced in 1942 and I submit my evidence

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Thank you, I would like to add that the A.P./I. MK. I. in the table was the HE round with over 8 grams of incendiary material inside and a hardened steel nose cap instead of a fuse. It seems to penetrate just as much "hard parts" as a .50 cal AP while distributing a fair amount of chemical at the same time.

Glider said:

This is so wrong its almost a new level and I would love to see any evidence to prove this and prove me wrong but admit to not holding my breath

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Great posts from you and SR6, the bolded part is gold dust

The standard laod from 1942 on was 50% HE and 50% API. The 20mm penetrated as much armour as the 0.5in and had the explosive content that the 0.5 so lacked. The Ball was being replaced in 1942 and I submit my evidence

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The 20mm AP/API was piercing more than .50 when hitting at oblique angles - about twice as much when impacting at 40 deg.

zjtins said:

The Jap copy was low rate, lower MV and far less effective than the M2, but so was their 20mm as compared to contemporaries. IMHO this gets real difficult since the japs were much more resource limited. If you look at the planes and armament planned near the end of the war, they were pushing 30mm as their choice. There 20mm setup was to heavy and not effective enough. But this really is whole new discussion as the Japanese experience.

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The Ho-103 was MARGINALLY less effective than the M2. Yes it fired lighter ammunition at a lower muzzle velocity, but it had a HIGHER rate of fire, was lighter and used HE and SAPI ammunition from the outset to make up the difference. In terms of punch per gun it was probably about 85% to 90% as effective as the M2.

I also wonder which of the five Japanese 20mm types you're referring to?

It should be noted that in 1943 the UK developed another version of the AP shell called APIII.

Details as follows
Penetration at 200 yards o degrees 67 mm at 30 degrees 48 mm
Penetration at 400 yards 0 degrees 51 mm at 30 degrees 38 mm
Penetration at 600 yards 0 degrees 39 mm at 30 degrees 30 mm

I don't think this APCR ammunition was used to any degree as it was designed as an anti tank weapon, but had penetrating armour been a problem they clearly had something in hand. It did enter production in 1943

zjtins said:

Go read bob Johnston P-47 book numerous examples of engine pieces blown off and plane got home. I never said the 20mm could not cause damage but the myth vs fact is more than one round in air cooled engine was needed to bring a plane down with a high confidence.
And no matter how much you quote technical specs that is not combat damage records the only true measure.

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Myth v fact = this was your original assertion:

zjtins said:

I find much of the info to date misleading. Comparing energy of chemical (explosive) vs mechanical is pointless. The do not have the same affect on a target.

A .50 solid bullet can destroy a water cooled engine in 1 shot. A 20mm thin shelled round may explode on the engine's surface and essentially do nothing.

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Yeah, right so the fact that Bob Johnson got home with pieces from his air cooled radial shot off proves what, exactly? I'm still waiting for your evidence that your initial claims are accurate

Aozora said:

I'm still waiting for your evidence that your initial claims are accurate

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Like his claim that the US Air Force used the .50 cal gun in fighters up until Viet Nam

He also seems to confuse the German 20mm mine shells with Hispano ammuntion a lot. Since the Hispano, or anybody else's 20mm gun, never used "thin shelled round"s I am not sure what the German shells performance has to do with a comparison of the .50 Browning and the 20mm Hispano gun.

I suspect that this thread has now run its course and zjtins will not reply further

Shortround6 said:

Like his claim that the US Air Force used the .50 cal gun in fighters up until Viet Nam

He also seems to confuse the German 20mm mine shells with Hispano ammuntion a lot. Since the Hispano, or anybody else's 20mm gun, never used "thin shelled round"s I am not sure what the German shells performance has to do with a comparison of the .50 Browning and the 20mm Hispano gun.

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We did have A-26's with the 8 fifty nose armament, and A-28's (T-28) with 2 fifties at NKP Thailand, in 1967. Not exactly fighters though.

Not that i'm trying defend anything ztjins is saying.

nasty discussion. I take it this is an attempt to refute the value of 20mm armamanet. havent got much to add, but would point out that the standard armement loadout as time progressed faovured 20mm cannon and tended to discard or reduce the 50 cal . a good example was the Sea Fury FB11, which went into battle (korea) with 4x20mm, and was considered by many to be one of the best GA fighter bombers of that conflict. 20mm remains standard for many aircraft to this day, 50 cal fits are rare. That to me says it all

Part of the ongoing dispute between advocates of the .50 and the 20mm is that the guns and ammo changed over time. They did not stay constant. And the vast variety of 20mm guns and ammo makes it very difficult to draw comparisons without being specific as to exactly what somebody is trying to compare.

The .50 cal gun and ammo did work in WW II, that does not mean it was the best. It did some things very well (or had some very positive attributes) but it had some negatives as aircraft armament. It was heavy and it's ammo was heavy, both negatives from an aircraft armament point of view. For destroying lightly protected targets (and few aircraft really carried a LOT of armor, single engine FIGHTERS rarely caring more than a few hundred pounds in a 5,000 to 10,000 pound (empty) plane) explosive ammunition was going to be better than solid rounds.

For aircraft the a major part of the criteria for good armament is just like an engine, you want a good power to weight ratio. You want the most destructive armament you can get for the least amount of weight. Destructive ability covers a lot of different things.
Range.
Destructive ability of a single hit.
Rate of fire affects both the likelihood of hitting and getting multiple hits.
Firing time.
Intended target.

I would also note that just for the .50 cal alone that while the weight of the gun stayed pretty much constant the ammo ( the real weapon, or at least the pointy end) changed considerably from the late 30s to Korea (M2 ball gained 400 ft per second in velocity and around 30% in muzzle energy over M1 ball) going through 3 if not 4 different incendiary bullets and the rate of rife roughly doubling with the M3 gun. The M3s in an F-86 Sabre also had a Gyro gunsight AND a radar rangefinder making comparisons to WW II fighters a little difficult. A Korean M3 .50 cal might be 3-4 times more effective than a 1940 M2 gun when counted on number of barrels alone. It had twice the rate of fire, more powerful ammunition, better incendiary rounds and better sighting equipment.
Of course the Korean 20mm guns had many of the same advantages but using Korean combat results to justify WWII combat effectiveness has way too many variables.

The .50 cal gun and ammo did work in WW II, that does not mean it was the best

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Thats another way of saying what I have been. It worked therefore not a major concern to switch so they did not.

The .50 cal gun and ammo did work in WW II, that does not mean it was the best

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Thats another way of saying what I have been. It worked therefore not a major concern to switch so they did not.


Also the F86 had fuselage mounted guns so effective range went out much farther. Another reason for then the .50 setup was acceptable.

Now this is interesting. Where that information can be confirmed, since it's as far from the truth as possible.

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Wow cant search or read The Supermarine Spitfire MkIX
F IX Merlin 61; 63 or 63A; two 20-mm. and four .303-in. guns.
LF IX Merlin 66; two 20-mm. and four .303-in. guns.
LF IX (e) Merlin 66; two 20-mm. and two .5-in. guns.
HF IX Merlin 70; two 20-mm. and four .303-in. guns.
HF IX (e) Merlin 70; two 20-mm. and two .5-in. guns.
PR XI Merlin 61; 63, 63A or 70.
F XVI Merlin 266; two 20-mm. and two .5-in. guns.
Appears about half were .50 options the other half everything else .

Comparing US .50 cal guns to foreign guns gets a lot harder. The 20MM MG/FF in a 109 weighed LESS than a .50 cal Browning as did the Japanese Navy type 99-1 cannon mounted in early Zeros.

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AN/M3 in aircraft .50 cal was 61 lbs vs 58 lbs for the MGFF so 2 lbs... wow
you also lose 290 M/S velocity (890 vs 600) which does (did) make a different in battle.

After the Fall of 1944 the NAVY did NOT ORDER an new fighter with .50 cal guns. All fighters armed with .50 cal guns delivered in 1945/46 had been ordered prior to the end of 1944.

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So a statement and no proof.