Vic Nighthorse
Airman
- 34
- Sep 9, 2018
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It is hard to imagine that this hasn't already be covered here and I apologize if it has. I looked but did not find. Is it true that the M4 37mm HE shell, as used in the P-39, only had 45g of tetryl (R.E. = 1.25) and that the 30mm German mine-shell had 85 grams of PETN (R.E. = 1.66)? If so, does that necessarily mean that the German shell was more destructive to aircraft? Thanks for your help.
Thanks, I had seen a cutaway of the 108/103 mine-shell but not the American 37mm. I imagine the mine-shell would be especially effective in a fuel tank where it could find more 'reaction mass'. Is it's fuse long enough to get inside the fuel? I also do see how the sectional density of the 37mm fragments would be a lot greater. The 37mm projectile itself, even though shorter, also has about a 22% greater sectional density and maybe explain why it it only has 300fps (or so) on the 108 mine-shell with a 'deeper' propellant charge and much longer barrel. I saw a BC of .442 for the mine-shell on Lunatic's WWII Aircraft Gun Ballistics Page which presumably came from Anthony Williams. Anyone know different and or know what the 37mm shells BC is? It looks like it has a lower drag shape than the mine-shell. Thanks, again Greyman that was very helpful.
It is hard to imagine that this hasn't already be covered here and I apologize if it has. I looked but did not find. Is it true that the M4 37mm HE shell, as used in the P-39, only had 45g of tetryl (R.E. = 1.25) and that the 30mm German mine-shell had 85 grams of PETN (R.E. = 1.66)? If so, does that necessarily mean that the German shell was more destructive to aircraft? Thanks for your help.
The M54 HE shell for the M4 - M10 37mm aircraft gun was the same used in the M1 37mm AA gun with a smaller cartridge case.
The M80 AP shell for the M4 - M10 37mm aircraft gun was a solid shot. It was a shortened version of the AP shell used in the M1 37mm AA gun.
( 37 mm gun M1 - Wikipedia and. 37x145mmR - Wikipedia and Cartridge, 37mm HE-T, SD, M54A1 )
Like many other things in life, designing an explosive shell seems to be a trade-off. Thinner walls and more explosive gives a bigger 'bang' while heavier walls and less explosive gives more shrapnel damage.
Shell for the M4 perhaps didn't needed to have thinner walls, but might've used thinner bottom and thus being lighter for barely any decrease of on-target effect. See the picture posted above for how thick the bottom was - going off-the-shelf can have it's shortcomings.
Lighter shell means faster shell, that in return can offer better trajectory and will be less incompatible with trajectory of the .50 BMG.
It all depends upon your theory of damage regarding the shell you are designing.
The US theory was to use the relatively thick shell walls as shrapnel to rip through the target aircraft's structure and/or crew. Also, I seem to remember the 37mm HE shell would still penetrate a quarter to a fifth of an inch of armor at 500 yards or so. If you want to bring down a bomber, the 37mm was designed specifically to do that. All other considerations aside, that's the shell you want on target.
Remember, asking 'which shell' is a different question than asking 'which gun.'
See just under, red is roughly the part that needs to go away. I'd also try to use a smaller fuse so there is either greater explosive content, or to reduce the weight down.
The part outlined in red includes the tracer and associated self-destruct mechanism (the shell blows up on tracer burn-out). You may not wish to be without those...
Yes, but those were not SD rounds - they had a very simple air-compression percussion nose fuze. An SD fuze is by definition a much more complicated device - and thereby much more expensive to make.The fuse containing self-destruction mechanism was a thing back in 1940s, though. Lack of the base-installed S/D member can be seen in this cutaway for the Hispano and big Oerlikon ammunition.
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SD in aircraft ammo was primarily useful for home defence planes, since they didn't want live shells falling on the heads of their own civilians. That was the Luftwaffe's view anyway - the RAF seemed less concerned.
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Let me try again.
My suggestion is to get rid of the too thick bottom of the shell. I didn't suggested thinner walls of the shell. The bottom of the shell is the part that is most likely not to hit anything in the target aircraft, since it will tend to go backward when detonation happens. Armor represented perhaps 1% of the target area on a bomber; people were introducing airborne cannons exactly to take advantage of the huge unarmored surface area of the perspective enemy bombers.
They say a picture is worth a thousand of words. See just under, red is roughly the part that needs to go away. I'd also try to use a smaller fuse so there is either greater explosive content, or to reduce the weight down.
View attachment 606137
The two questions are as connected as possible. A 25-30 kg automatic gun can be perfectly fine for firing a 90-130 g shell (typically 20mm) at reasonable muzzle velocities; there were historical weponns back in the ww2 that did exactly that. Trying to come up with an automatic gun that fires 650-800 g shell at reasonable MVs on 25-30 kg will not work. The 25-30 kg gun and it's ammo can be installed on most of fighters from second half of the 1930s without much of problems (even on the small Bf 109, I-16 or MB.152), not the case with a 100 kg gun and it's ammo.
The part outlined in red includes the tracer and associated self-destruct mechanism (the shell blows up on tracer burn-out). You may not wish to be without those...