37x145mmR HE shell vs 30×90RB mine-shell

[Vic Nighthorse]

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.

 

[tomo pauk]

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.

It might be so that 30mm M-shell have had more explosive - that was the point of whole M-shell saga, Germans were making thin-walled shell cases from pressed metal (= more HE content in %), just like the cartridge cases, while all others were drilling holes in metal rods, that resulted in thick walled shell cases (= less HE content in %). However - the 'traditional' shell will release much heavier shrapnels, that stand better chance to go through skin, stringers and other metalic part of aircraft and do additional damage. At the end of a day, an aircraft that received 2-4-6 shells from the 37mm M4 cannon and the other A/C that received 2-4-6 M-shells from German 3cm cannon will likely go down in similar fashion, or at least suffer severe damage in case the target A/C is a tough animal, like the B-17 was renown to be.

 

[Vic Nighthorse]

I had considered that a thicker shell wall would produce larger more penetrating fragments but was stuck on the notion more energy meant more work done. Thinking about it now, I realize that that was an over simplification. Thanks for responding. I wouldn't mind hearing from others about their thoughts on the relative merits of those shells if they are so inclined also.

 

[Greyman]

Quick n' dirty sketch for the heck of it.

 

[Vic Nighthorse]

Quick n' dirty sketch for the heck of it.

View attachment 510806

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.

 

[alsaad]

One thing that very small number of people takes into account is the fuze delay. Instantaneous fuzed shell will provide less damage than 0,05 sec delay fuzed shell as first one will explode on and other in the target where any type of projectile will cause significantly more damage. Germans figured that our, Russians too.

 

[Shortround6]

I think you will find the British figured it out too.
Actually figuring it out was relatively easy. Getting a high percentage of the fuses to act like you want them to is hard part.

 

[Greyman]

Not to mention at different ranges (striking velocities).

 

[alsaad]

Every fuze has more or less unwanted delay due to its components reaction on impact but that reaction is still quick enough, aprox. 5/1000 sec, to cause detonation on the skin. The real problem of the efficient delay is in the design of the delay mechanism in the fuze and in fuze strength to withstand stress upon contact with the target and prior to set off. Most of the WWII era fuzes used black powder pellet as a pyrotechnical delay element which provided constant delay time with small tolerance from one piece to another which could give somehow different effect on the target depending on the projo velocity on impact. Germans experimented with dynamical delay in AA and aircraft ammo (and used it in big scale on 88 AP-T rounds) which set off the round upon the penetration of the skin due to mechanical delay. I really do not have any data on use and the effects of these fuzes except they are very sensitive if found unexploded. Other problem might be the strength of the fuze as it might be torn of the round in that 1-5/100 sec of the delay length especially if it is activated on soft skin and hits something hard just after it...but that problem is more theoretical than practical.

 

[jmcalli2]

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.

Note that reports of the power of the US 16" HC rounds with 'only' 70lbs of explosive in Vietnam; "The High Capacity (HC) shell can create a crater 50 feet wide and 20 feet deep (15 x 6 m). During her deployment off Vietnam, USS New Jersey (BB-62) occasionally fired a single HC round into the jungle and so created a helicopter landing zone 200 yards (180 m) in diameter and defoliated trees for 300 yards (270 m) beyond that." ( NavWeaps | Naval Weapons, Naval Technology and Naval Reunions )

(To my knowledge there has been no attempt to adapt the 16" Mk 7 into an aircraft gun. LOL)

You can see the different shell design philosophies here, also from navweaps.com

US 16" AP Mk 8 2,700lbs bursting charge 41lbs
HC Mk 14 1,900lbs bursting charge 70lbs

12" Mk 8 AP Mk 18 1,140lbs bursting charge 17lbs
HC Mk 17 940lbs bursting charge 79lbs

British 16" AP Mk 1B 2,048 lbs bursting charge 51lbs
HE 2,048 lbs bursting charge Not available

15" AP Mk 1A 1,920lbs bursting charge 61lbs
HE 8crh 1,965lbs bursting charge 224lbs

14" AP Mk VIIb 1,590lbs bursting charge 48.5lbs
HE 1,590lbs bursting charge not available

German 15" APC L/4,4 1,764lbs bursting charge 41lbs
HE L4,5 1,764 bursting charge 72lbs

Japanese 16" AP Type 91 2,249lbs bursting charge 33lbs
HE Type 0 2,069lbs bursting charge 98lbs

18" APC Type 91 3,219lbs bursting charge 75lbs
HE Type 0 2,998lbs bursting charge 136lbs

 

[tomo pauk]

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.

 

[jmcalli2]

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.'

 

[tomo pauk]

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.

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.

Remember, asking 'which shell' is a different question than asking 'which gun.'

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.

 

[A.G. Williams]

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...

It's worth mentioning that not all of the M-Geschoss were the same: the ones shown so far were the original Ausf.A pattern. The Ausf.C (which only saw aircraft use in 30 mm calibre) was less extreme, with a more solid base and a more pointed nose. This had better ballistics (and could have a tracer) at the cost of a small reduction in HE (from c.85 to c.75 g).

It is also worth considering that only one country had both conventional and M-Geschoss rounds available for their major cannon, so could make direct comparisons of effectiveness - and they preferred the M-Geschoss.

 

[tomo pauk]

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...

That's fair enough.
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.

 

[A.G. Williams]

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.

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.

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.

It was AA guns which made the most use of SD ammo, partly for the reason given above, and especially in warships (didn't want to accidentally shoot up a distant friendly ship).

 

[tomo pauk]

...
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.
...

Germans seem to be all over the map.
They have had both pyrotechnic and mechanical SD element employed, but they also made shell types (at least for airborne guns) that were without the SD element. Mechanical SD element was (exclusively?) used in the Mine shells, but there were also Mine shells without a fuse that had SD element.

 

[Greyman]

Looking at ammunition proportion tables re: different types of missions -- the general rule for the Luftwaffe appeared to be:
- air combat: SD ammunition
- ground attack: non-SD ammunition

Which makes sense.

 

[jmcalli2]

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.

I understood the bottom of the shell. Considering the smaller cartridge used by the M4 - M10 37mm aircraft cannon, you may have a point; the shell was designed for the larger propellant charge used in the 37mm Anti Aircraft gun.

As for which gun, my point was only that when you are talking about which gun to use in an aircraft, things such as mission, likely targets, size, weight, and structural considerations come into play. When you are talking about which shell for a given task, you are talking about the shell and the target only. An interesting resource for that is: The WWII Fighter Gun Debate: Gun Tables
They have some interesting ways to compare guns.
A little disappointed the 75mm used on the B-25 was left off of that site though.

 

[jmcalli2]

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...

The fusing/tracer likely goes back to the M54 37mm shell (not the entire cartridge) being an Anti-Aircraft round. Just a guess.