Forum member Neil Stirling posted this on another forum (I would link to that thread but the forum is for members only). Its from a PRO document, Neil didn't provide the exact reference:
In its first form the gun fired about 600rpm and was found by the RAF to have severe limitations. The barrel was not capable of sustaining long bursts of fire, there were numerous stoppages due to inherent faults in design and breakages of components occured very early in the life of the gun.
The major fault was the poor life of the gun barrel and after a few rounds fire became completely inaccurate. reports of numerous trials were presented to the U.S Army Ordnance Corps but, since at the time the USAAF had but little operational experience and the complaint that worn out barrels should be replaced, despite the fact that it was impossible to replace barrels when a aircraft was in the air and that the supply of spare barrels might present problems during advanced operations. Caused the US army Ordnance Corps to develop an improved .50 Browning machine gun. This gun known as the T.36 had a rate of fire of 750rpm to 850 rpm and was designed to overcome the defects of the earlier model which had come to light in operations. The first T.36 guns became available in early 1944.
The following is quoted fromm the JFC in that same thread by Hop (AH poster Nashwan):
In addition to that you have one more great advantage - that is you can have longer and more frequent bursts without damage to the gun with the 20 than you can have from the .50 cal. That is important for the strafing airplane, because they are burning up their barrels and ruining their guns on one flight. Sometimes it is long before that one flight is over. They will come down with screaming barrels and get trigger happy, and then all the barrels are gone in one flight. It should not happen in a 20mm.
Butch provided this scan from the 'US late 1944 Aerial Gunnery manual':
Poster, but now Persona Non Grata, Kurfürst posted the following scan from the Standard Ordnance Catalog:
Emmanuel Gustin posted:
There were two separate, important modifications: The increase in the rate of fire, around 1940, and the introducted of stellite-lined and chrome-plated barrels for the M2 aircraft gun, very late in the war. Barrel wear was recognized as a serious problem with the .50, and much effort went into designing a more wear-resistant barrel. But I don't know whether these barrels would have been available to the RAF (if only for testing) in early 1944.
A maximum 75-round burst (from a cold barrel) may not sound as a big restriction, but with the 2% to 5% hit rates typical for most pilots, it would only result in somewhere between 1 and 4 hits. The answer was to install large batteries of guns --- fortunately the USA built bigger fighters with more powerful engines than everyone else, so it wasn't such a big problem as it could have been.
I suppose the advantage of the Hispano HS.404 series in barrel wear would have been largely due to the projectiles having dedicated copper driving bands, while machine guns usually (not always) engage the rifling with the jacket of the projectile. But for the same effect on target the Hispano needed to achieve only a quarter of the hits, so it shorter bursts were likely to be fired anyway.
Hohun posted:
I just found the following information (Flight Journal, Special Issue Winter 2000):
"20mm cannon versus .50-caliber guns
In Monroe's - discussions, it became apparent that the British and the U. S. Navy were in the process of making a switch from .50-cailber guns to 20mm cannon. The principal reason was that although the 20mm cannon had a slower rate of fire, it put out more weight of metal than the .50-caliber gun in a given time, and it did not jam during a 20-second, full-load burst [**]. The U. S. Army was the prinipal aircraft-gun developer here. The Army Air Corps personnel who attended the conference adamantly held to the position that to get more lethal density from the configuration, .50-caliber guns must remain the wing-mounted armament. The 20mm would be tolerated only for the centerline gun installations such as those in the P-38 Lightning and the F7F Tigercat. As the discussions progressed, we were to see many more adamant, opinionated service doctrines."
* Cdr Jack Monroe, Chief of the Ordnance Branch of the Navy Bureau of Aeronautics, apparently responsible as host for the Joint Fighter Conference's ordnance discussions.
** For comparison, jamming was expected for .50-caliber guns in "bursts that exceeded five to 10 seconds".
poster hoarmurath wrote:
I have noticed a reference to length of bursts in the booklet written by Lt Col Westbrook that have been posted at Ring' Pro Doc site:
II. BASIC TACTICS
1. Aerial Combat.
Following are a few points on aerial combat which should be habits while in the target area.
a. Look around
b. Stick together
c. Stick with your element leader. Should you lose him join with anyone. The pilot who is careless about getting off by himself will get it sooner or later.
d. An immediate attack is the best defense. If you have an even to better altitude advantage tangle with anything up to twice your number.
e. Don't try to turn with the Nip. It can't be done in any Allied aircraft. Break off when lead can no longer be held. At slow speeds (200-220) this will be approximately 40-50 degrees of turn. At high speed (350-375) as much as 180 degrees.
f. Be prepared for his turns on your approach -- starting shallow and then "reefing in" as you close within range.
g. Turn into the attack.
h. Keep up speed -- it's the big advantage.
i. Hold fire until within range. Bullet drop, loss of impact force, and dispersion make long range shooting impractical.
j. Try for a low quarter 10-20 degree deflection stern attack after driving down slightly below and behind him.
k. Don't rely on tracer or deflection shooting. Use the gunsight.
l. Allow an extra 1/4 to 1/2 ring when 2 "Gs" or more are being pulled on pursuit curve. Error the long side.
m. Bullet drop is not compensated for when you're in a bank -- you must aim high on the line of flight -- as along top of Nip fuselage.
n. Our planes are equipped with gun booster. The rate of fire is so increased that a four second burst will burn out the barrels on the first burst. Succeeding bursts must be reduced in length to two second maximums if firing is in quick succession.
o. If a Nipper catches you turn away from your element leader so that he will be able to turn into the Nip. Do this while pulling into a shallow balls-out climb or dive using plenty of evasive action.
p. The Nipper's favorite evasion is the split "S" close to the ground -- don't let him "auger you in"; it's been done!
q. If you are latched badly while on escort drag the Nipper across close to the bomber formation and let their guns brush him off.
r. Stick together.
The article can be found under 'US combat tactics'.
Felix99 wrote:
In "British Aircraft Armament - Vol. 2" by R. Wallace Clarke, the author notes, as Emmanuel says: "With minor improvements, the M2 armed nearly all US warplanes in the Second World War. One of its drawbacks was short barrel life: the ammunition was not fitted with the usual driving band, and when armour-piercing rounds were fired, the hard metal soon wore down the rifling. However, this was not seen as a major problem, and the supply of barrels was always adequate."
Hope this helps,
Felix
Pro-longed bursts seem to have caused concern in regards to several issues the main being barrel wear and jamming.
I was just reading several pilot accounts of Ami pilots during Bodenplatte (Jan 1 '45) several pilots commented on being caught up in the excitement of the attacks they held down their fire at one or two LW fighters running out of ammo. There's was mention of 4 or 6 sec burst with all guns. Then the pilots 'kicking themselves' for wasting so much ammo. There was no mention of jams / cook-offs etc...
With the hundreds of LW fighters flying OTD at 50 meters with their radios off and orders not to dogfight (push through to target) had these Ami pilots been more frugal with their ammo they would have most likely earned more then the 1 or 2 kills they did get. For most of these pilots this was there first and only up close contact with the enemy. LW fighters had become extremely rare at this point during the war.
