Ammunition was issued in the form of fixed rounds, consisting of H.E. shell, M54, with P.D. fuse, M56; practice shell, M55A1, with dummy fuse, M50; and A.P. shot, M80.
The rapid strides in aircraft protection made it necessary to develop an aircraft weapon that would fire projectiles with greater explosive and armor-piercing qualities than smaller caliber weapons. As a result, the 37 mm (1.46 in) automatic gun, M4, was developed and standardized for aircraft use.
The 37 mm gun (1.46 in), M4, used the same high-explosive (M54) and practice (M55A1) projectiles as the 37 mm (1.46 in) antiaircraft gun, M1A2, but different cartridge cases are necessary due to the larger chamber of the M4 gun.
However, the overall length of the armor-piercing projectiles, M51 and M74, which were used in the M3A1, M5A1 and M6 tank and antitank guns, was too great to permit their use in the M4 gun and the 37 mm (1.46 in) armor-piercing shot, M80, was developed and standardized.
M54 37mm Cannon Shell - High-explosive shell, 37 mm, M54 standard
This shell used the M56 point detonating fuse. The complete round weighs 1.99 lb (900 g); as fired, the projectile weighs 1.34 lb (608 g). The 0.16 lb (70 g) charge of M2 powder is a Hercules NG formula of single perforated grains with 0.030 in (0.76 mm) web and gives the projectile the prescribed muzzle velocity of 2,000 ft/s (610 m/s).
The M54 used a shell-destroying tracer in addition to the point-detonating fuze. The tracer had a burning time of three seconds at the end of which it set off an igniting relay charge of 1.68 gr (0.109 g) of Grade A-5 Army Black Powder which ignited a relay pellet that detonated the charge, destroying the shell before ground impact.
The bursting charge of tetryl weighed 0.10 lb (45 g), and the alternate Composition "A" charge weighs 0.105 lb (48 g). The tetryl loading consisted of a 200 gr (13 g) tetryl pellet pressed into the shell cavity under 9,000-10,000 psi (60-70 MPa) pressure and the remainder of the charge of two equal increments pressed under approximately 9,000 psi (60 MPa) pressure. The Composition "A" bursting charge is loaded in the same manner as the tetryl charge, except that the relay pellet with the Composition "A" weighs 36 gr (2.3 g) as against 23 gr (1.5 g) for the pellet used with the tetryl load.
Armor-piercing shot, 37 mm - M80 standard
The AP shot was a monoblock projectile with a tracer element of three seconds burning time. It did not need a fuse or bursting charge. The weight of the complete round was 2.31 lb (1.05 kg), the weight of the AP shot was 1.66 lb (750 g). The propelling charge was 0.15 lb (78 g) of M2 powder of a Hercules NG formula with a single-perforated grain and 0.030 in (0.76 mm) web.
A. S. Was a 37mm cannon necessary? Wasn't this too large a caliber for a fighter? You had so few rounds of ammunition. And wasn't its rate of fire slow?
From an interview with a Soviet P-39 Pilot. - http://lend-lease.airforce.ru/english/articles/golodnikov/part3.htm - about 1/3 down page
N. G. One cannot say that the 37mm cannon was a disadvantage or an advantage. Look at it from this perspective. The M-6 [this is incorrect; it was M4] cannon had its strong and weak points. One had to take advantage of the strong points and compensate, as much as possible, for its weaknesses.
These were the weaknesses: 1. Low rate of fire. 8 rounds/second [this is incorrect; the correct rate is slightly over 2 rounds/second (130 rounds/minute) - J.G.] This is indeed a low rate of fire.
2. The ballistics of the projectile were abysmal. The flight trajectory of the projectile was arching, which required large lead angles. But again this was at long ranges, especially when firing at ground targets. When firing at ground targets we had to apply two rings of the sight for lead.
3. Minimal ammunition supply. Thirty rounds.
All these deficiencies could be compensated for by proper selection of firing range. If one fired from 70-50 meters, there was sufficient rate of fire, the ballistics at this range were acceptable, and the lead required was minimal. Thus, all the weaknesses of the 37mm cannon listed above revealed themselves only at long ranges.
Now regarding the strengths: 1. The projectile was very powerful. Normally, one strike on an enemy fighter and he was finished! In addition, we fired this cannon at other types of targets. Bombers, vessels at sea. The 37mm cannon was very effective against these targets.
It appears there should be 2 different rounds to choose as a load out as the other aircraft that have this option available. The complaints about the weapon is the loopy trajectory, slow firing and small ammo load. With it being a short muzzled, low muzzle velocity weapon this would seem a true description of the weapon.