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

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I think that's more to the point regarding 7mm rounds, however i take the word "capable" to mean that it can, but not all the time.
I show a ball round of 7.7mm going through 8mm of armor at 200 yards, and M2 50 cal going through 20mm at the same range.
At 600 yards the M2 still penitrates up to 16mm of armor plating and that's where your benefit is in having a heavier round.
Need i address 20mm AP at 600 yards?? ok... that goes through 23mm at that range.
However the HE 20mm (Hispano Mk I) doesn't get beyond 8mm at 200 yards.
You can make guesses on oil pan shots or cracking engine blocks, and the answer would be that the 7.7mm is capable.
However any off angle shot gave no results, where the 50 cal still penitrated beyond 12mm at the same range.

For that reason pilots probably saw more consistency with their shots over a variety of ranges as well as a variety of targets, something where 7.7mm probably would have a much narrower use in air to air or air to ground applications.

You can find that data on this forum under the 50 cal vs 20mm thread.
 
How does it come that the Beresin B-20 Machine cannon is so good with so little weight? Why were the other guns so heavy compared to it?
Would it have been possible for the other guns to save more weight?
 
Edgar:
I guess I should have said 'B' armament, rather than B wing. Most MkIX's for example had B armament configuration of 2 x 20mm + 4 x .303, even though they had 'C' wings. I do have Morgan and Shakladys book, among others.
BTW, (as I'm sure you know) the Spit 21 had a very different wing, which the 4 cannon armament worked reliably in.
 
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Shortround6 said:
It may have been a pre war calculation that figured a 3 second burst was needed, or that a pilot could only stay on target for 3 seconds that lead to those charts that show how much weight of projectiles could be fired in 3 seconds. .
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Shortround it was a pre war calculation that 2 seconds was as long as they thought a fighter could bring his guns to bear and 4 x 303s wasnt enough so they doubled it to 8 x 303s. this was done by SL Ralph Sorely posted to the Operational requirements branch of the Air Ministry. In apr 1935 they modified the spec for the monoplane fighter to as many guns as possible but suggested 8 as
 
spicmart said:
How does it come that the Beresin B-20 Machine cannon is so good with so little weight? Why were the other guns so heavy compared to it?
Would it have been possible for the other guns to save more weight?
Click to expand...

Part of it was the expected service life. The Hispano was originally designed to have a life of 10,000rounds. This was later cut to 5,000rounds with the MK V and the higher rate of fire. Part of the Browning .50cal reputation comes from it's reliability/durability.
The Russians accepted a much shorter service life from their guns and were able to make them lighter. As long as the supply of spare guns can be maintained it is not a bad plan, and with many aircraft being shot down or crashing well before their guns wore out it looks even more attractive.
Gun life is not barrel however, don't confuse the two. Both the US .50 and the B-20 are going to need plenty of spare barrels if the pilots fire long bursts.
 

Thank you, I was trying to figure out were the comparisons of weight of projectiles fired in three seconds come from.
 
Shortround6 said:
Part of the Browning .50cal reputation comes from it's reliability/durability.
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My understanding is that there was a problem with the 0.5 when used in GA. The problem was the overheating when used in a long burst over about 6-7 seconds, the gun basically seized solid. In Air to Air combat that chances of a long burst are slim and the danger of a jam remote. On a GA run particularly if you are trying to knock out AA guns and/or have a juicy target in front of you, the temptation to keep the trigger down was a lot higher. The result was often the pilot getting back screaming blue murder at the ordinance staff complaining that their guns wouldn't work.
To avoid overheating the limits for the 0.5 was a 75 round burst followed by no more than a 25 round burst.
This problem didn't happen with the 20mm as more of the heat was retained in the shell case and removed from the gun when the case was ejected. The 0.5 case didn't retain as much heat and when the case was ejected the residual heat was retained in the gun ending up with a jam if the burst limits were exceeded.
 
Part of the .50 cal reputation comes from it's use as a ground gun, both AA and against ground targets from tripods but usually vehicles. The Ground guns had lower rates of fire and heavier barrels. Granted there was no slipstream to help cool them but then a lot of the ammo boxes were only 100 rounds so even it it was fired in long long burst there was a bit of break while while a new belt/box was fitted. Cycle rate was 450-550rpm and it used a 45 in barrel that was much heavier than the 36in aircraft barrel, hence the M2 HB (heavy barrel) designation. I dare say a number of the forum members have seen this gun fired or even fired one themselves.
It is not that the aircraft version was flimsy or anything (they can be converted from one version to the other with the right barrel/shroud and a few parts) but aircraft mountings do present some problems not seen by the ground guns.
They are long lived, rugged guns but pay for it in weight.
 
My own expierience of the M2 was one of short bursts to keep the barrel temp down, as the gun heats up it does get prone to ejection stoppages, the armourer instructing us told us you had to listen to the gun go out of tune when firing it and cease fire before it jammed up on you, and by jammed, by eck thats exactly what I mean!
 
"They are long lived, rugged guns but pay for it in weight. " Well, Shortround6, no argument regarding the beginning of the comment regarding the robust construction of John Moses Browning's .5 inch M2 machine gun. Considering the topic of the thread compares the 20mm virtues and vices the M2 weighs considerably less, both in initial weapon weight, recoil and ammunition. Used as an airborne weapon cooling at the lesser cyclic rates poses little threat of malfuction due to the effects of heat. Ground guns used in a high ambient temperature enviornment might leave one grabbing the shoulder or side arm in a hot corner. Three round bursts and mark your target. Regards
 


Thanks for the response.

regards
 
Compared to the Russian B-20 the Browning offers less of cycle rate (until the M-3) using slightly less powerful ammunition for a lot more weight. Maybe the longer life was worth it, maybe it wasn't.

Comparing the Browning to the Hispano, both were heavy long lived guns. Once the plane could lift the weight the Hispano was a better choice than the M2 aircraft gun. While the gun weighed about double as did the ammo each round had three times the kinetic energy and some of them exploded to boot. At any practical air to air range (600-1000yd shots were by far the exception in WW II) there isn't enough difference in trajectory or time of flight to get real exited about. Going with the US Navies assessment that one 20mm equaled three .50 cal machine guns the .50 doesn't really come out on top for weight vs effectiveness.

While the gun itself may or may not have stood up to heat depending on air temperature and slipstream the barrels of the aircraft .50s could be wrecked in short order by careless pilots regardless of atmospheric conditions.
 
We have all heard/read stories of American pilots having 5 or more kills, (9 for David McCampbell is the most I've read of), on one sortie. Every one of them were armed with Browning 50's. I would attribute that to enough power to kill the target with a short burst, and plenty of ammo for ALOT of bursts. Are there stories of British pilots getting 5 or more kills in one sortie with either LMG or 20mm cannon?

It's not that I don't think 20mm cannon are effective, you have got to have them for heavy bombers, the Germans couldn't have done without them. I just think the Browning 50, had the perfect combination of power and ammo capacity for engaging the targets Americans engaged at the time, which were, for the most part, small, single engine fighters, with a few exceptions now and then. If you are engaging large, 4 engined heavy bombers, there is no substitute for a 20mm or larger cannon. In fact, nearly all American twin engined bombers needed cannon to effectively kill them. American and British fighters simply had no target worthy of using 4 20mm on. A 3 second burst from 6 50's firing 800 rpm each, if on target, should bring down any single engine fighter we faced. In fact, it should bring down nearly any single engine fighter on any side built during the entire war. When you get into, mid to late war American fighters carrying 400 rpg with 6 or 8 guns, that gives you a considerable amount of time to miss your target, along with enough power to kill it should you actually be a good enough shot, or lucky enough shot, to hit it.
 

And McCampbell's Hellcat carried 720lb of ammuntion. More than weight than the guns, ammo, gun site and few other bits and pieces in a Spitfire. An eight mg Spitfire carried 440lbs of guns and ammo together. A Spitfire with two 20mm guns and four Mgs carried 650lbs of guns and ammo. The Hellcat carried 433lbs of guns in addition to the 720lbs of ammo for a total of 1153lbs. It is little wonder they had more combat endurance or firing time. 720lbs of ammo is enough for 290 rounds of 20mm ammo for four guns. I wonder how many planes a Plane with four 20mm guns and that amount of ammo could shoot down in one flight?

400rpg/13rps= 30.77seconds of firing time
290rpg/10rps=29 seconds of firing time.

BTW, when Hellcats replaced the inner .50 cal with a 20mm gun they carried 225 rounds of 20mm ammo per gun and kept the 400rpg of .50cal ammo.
 

How many rounds per gun did the Typhoon/Tempest carry?

Could the Spitfire have physically carried any more ammo? Was the wing big enough?

Were there very many/any aces in a day for Britian when they had 8 LMG or cannon?
 
Its worth remembering that it was the USN who were keen to get the 20mm installed on their aircraft. They firmly believed that the 20mm would do more damage, in less time than an aircraft with the 0.5 M2. For the USN this was very important. If the USAAF missed a bomber that gets through to hit an airfield, its almost a case of so what, the airfield will survive. If a bomber is missed and gets through to hit a carrier, then life is far more serious.
 

I agree the US navy had much more to lose, but, even with them, looks to me like the only real threat that might have required cannon would have been the twin engine Betty bombers and such. Even those were relatively easily destroyed. Weren't Betty's the type of aircraft that Butch O'Hare shot down 4 or 5 of in less than 2 minutes using an F4F3 Wildcat to win the Medal Of Honor?

McCampbell shot down 9, or at least he claimed 9, supposedly there were others that fell that he didn't claim. Would a cannon equiped fighter have enough ammo to do the same thing?
 
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pinsog said:
How many rounds per gun did the Typhoon/Tempest carry?
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140/150rpg.

pinsog said:
Could the Spitfire have physically carried any more ammo? Was the wing big enough?
Click to expand...
Not much more, even the MK 21 with the new wing and 4 guns only carried 175rpg for inboard and 150 rpg for outboard guns. Of course a MK 21 weighed less with with full tanks and ammo boxes than a F6F-3 did with empty fuel tanks and ammo boxes.
pinsog said:
Were there very many/any aces in a day for Britian when they had 8 LMG or cannon?
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No but that proves what? That 1100lbs of armament is better than 500-750lbs of armament?

The top score in a single day in Europe was by George Preddy, 6 fighters in one day, perhaps conditions in Europe were a bit different than in the Pacific?
 

The USN certainly believed that the reply is yes, it would do the same damage in less time.
 
Just to remind everyone, the AAF was not hepped up on the 20 MM cannon as I posted earlier and it had little to do with the lethality of the 50 BMG versus the 20MM but rather the amount of bullets a fighter could put into the space the enemy occupied. As an aside, regarding the ground use of the 50BMG against E/A, if one looks at film of early WW2 the AA 50 BMGs had water jackets just like the Vickers and Browning 30 cals had.

There have been several statements about whether the different ballistic properties of the projectiles of the 50s versus the 20MMs caused problems. The AAF thought those different properties were a real problem and disliked mixed armaments on wing mounted guns. This from the Fighter Conference Report.
 
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