Explosive ammo for HMGs - what is the verdict?

[tomo pauk]

Germans, Italians and Japanese used the explosive ammo for their heavy MGs during the ww2. Is there an assesment of how good actually that type of ammo was worth it vs. a (probably) simpler and cheaper API?

Paging also A A.G. Williams

 

[Shortround6]

You probably have seen this already. The Japanese and Italian projectiles were much the same.
The tracer compartment took around the same amount of space as the HE had for space.
Fuses and the labor needed to make such small projectiles with so many parts was going to be expensive.
Japanese had a simpler fuse but I don't know if it was early or late. Ki-43s had steel tubes/troughs (armor ?) under or in front of 12.7mm guns to protect the engines from pre-matures . I don't know what the damage might be but even a cut spark plug wire might be a problem at times.

For the Japanese army and the Italians is the 12.7mm guns or nothing which might have had something to do with it, until the JAAF got their own 20mm cannon.
For the Germans the 13mm as a defensive gun the ammo may make sense. For a cowl fighter gun with a shell firing cannon in the Prop hub perhaps less so.

Like a lot of this stuff, it depends on what the bullets actually hit
from a manufacturing standpoint, a 20mm using about the same fuse (same number of parts, just a bit bigger?) you will get around 3-4 times the "bang" for about 4 times the rare material but a lot less labor cost per big bang.

 

[PAT303]

Machine gun ammunition is too small to make it worthwhile, better off to use incendiary in them and leave explosive ammo to cannons.

 

[ThomasP]

Somewhere on the internet . . . there is a document by either the Bureau of Ordnance or USAF or DTIC or ?, that analyzed the Italian and Japanese HMG explosive rounds. I do not remember the details except that the fuzes were surprisingly (to me) simple and effective.

 

[z42]

Wikipedia mentions that a current day HE+API .50 BMG round costs a whopping $65 each. Imagine the expense of a P-47 8xM2 or a minigun firing these would be.

From an ammunition cost-effectiveness perspective I guess the optimal would be something with enough punch to shoot down a fighter with a single hit. So a 30mm basically, or perhaps a hypothetical 25mm class shell would be sufficient. Of course there are other factors as well in the total cost effectiveness of a weapon system, and a 25mm+ autocannon with good muzzle velocity and rate of fire was likely too bulky to mount on a WWII fighter.

Raufoss Mk 211 - Wikipedia

en.m.wikipedia.org

 

[Shortround6]

There is a lot information on the War Thunder forum.

Dysfunctional HE rounds for 12.7mm Ho-103 and Breda-Safat Machine Guns

First, a screenshot from the War thunder wiki showing the damage numbers. As you can see, according to the fifth row, the shell deals incendiary and fragmentation damage, rather than the explosive and incendiary damage which is it supposed to inflict. Right now, what we have ingame on these guns ...

forum.warthunder.com

The question being " Is there an assesment of how good actually that type of ammo was worth it vs. a (probably) simpler and cheaper API?"

the ammo was probably more effective on a per round basis. With only two guns per plane (many Italian the Ki-43s and some Ki-61s (+ tww 7.7mm) it may have been a good option/choice.

US fighters were firing 2-6 times as many bullets per second and didn't need quite the same amount of destructive power per bullet.


The US bullets were cheaper per bullet/projectile compared to the 12.7mm HE tracer round.

A lot of threaded brass parts in the fuse holding everything together.

US .50 ball or AP had 3 parts, the gilding metal jacket, the small amount of lead at the tip and the steel penetrator/body. Difference between the AP and the ball ammo was that the AP used a heat treated hardened penetrator of exactly the same shape/weight as the ball projectile. Simpler to make they do not get. Tracer gets the same sort of 3 piece cup the 12.7mm X 81mm round got stuck in the rear end.
However the US ammo used a much bigger cartridge case and almost twice as much powder.
A P-47 with full ammo was carrying 116lbs of gun powder in it's wings and and was going to dump over 410lbs of brass alloy out of the cartridge chutes

perhaps other countries didn't have the luxury of using up raw materials at such a rate?

 

[Denniss]

In short many Axis nations favored bullet power over "power of the bullets" just like they favored centerline guns ws wing gun batteries.

 

[Shortround6]

In short many Axis nations favored bullet power over "power of the bullets" just like they favored centerline guns ws wing gun batteries.

Perhaps.
The US shifted to the 6 gun .50 cal battery in 1940 with little (no ) combat experience. It took a while for the engine power to catch up but with the R-2800 engines really coming on line in 1943 6-8 gun batteries with large quantities of ammo could be carried while not sacrificing high performance.

You also had the fact that the US had screwed up 20mm Hispano production and so didn't have a good alternative. Not to mention you can't stick a cannon down the V of either the Allison or the Merlin without extensive redesign so we are getting into the chicken or egg argument.
Did the US go to wing batteries because they didn't have any engines that would take more than about 2 fuselage guns or did the US build engines that couldn't use prop mounted guns because they had decided in the mid 30s to use wing mounted guns?
Or P-39s with a nose full of guns and stick the engine behind the pilot?

The US also tended to use bigger wings on their fighters than axis nation fighters (and Russian) so they had more room to stick wing guns in.

 

[Denniss]

I believe the US .50 lost a lot of RoF to synchronization so they mostly discarded this idea.
Did the soviets develop explosive ammo for their 12.7mm guns? They were often used as centerline sync gun.
The US Hispano was a mega fail indeed - no idea why they so totally fucked-up this gun, an easy change could have cured it. Smells like a buerocrat as head of development/production. Gladly the P-38 guns were manufactured to british specs.

 

[tomo pauk]

Did the soviets develop explosive ammo for their 12.7mm guns?

Seems like they did, but post-ww2?
FWIW

Gladly the P-38 guns were manufactured to british specs.

Were they?

 

[Jabberwocky]

From the first hand accounts from Italian pilots I can recall, they were generally enthusiastic in the early war about the damage that HE ammunition did against RAF single seat fighters and medium bombers (Hurricanes, Spitfires, Kittyhawks, Gladiators, Blenheims, Bostons/Venturas and the like). Italian pilots also thought that the Breda-SAFAT gave them enough range to shoot at British bombers from outside of effective range of the .303 defensive guns.

I think there's some references in Hurricanes over Malta and (maybe) Spitfires over Malta about how much damage the HE rounds could do to RAF fighters. Here's a picture of a Wellesley that reportedly got hit by a couple of CR.42s:

[Photo] Pilot Officer Kennedy of No. 47 Squadron RAF Detachment inspecting his Wellesley bomber after engagement with two CR.42 fighters, Agordat, Eritrea, 25 Mar 1941; his gunner Sergeant German was killed

[Photo] Pilot Officer Kennedy of No. 47 Squadron RAF Detachment inspecting his Wellesley bomber after engagement with two CR.42 fighters, Agordat, Eritrea, 25 Mar 1941; his gunner Sergeant German was killed

ww2db.com

However, the tune seems to have changed when US four engine heavy bombers appeared in theater. The combination of bigger tougher aircraft and heavier defensive armament meant the Italian pilots started demanding heavier armament (20mm) for their own aircraft.

 

[Jabberwocky]

The US Hispano was a mega fail indeed - no idea why they so totally fucked-up this gun, an easy change could have cured it. Smells like a buerocrat as head of development/production. Gladly the P-38 guns were manufactured to british specs.

I'm not sure that's correct. As I remember it, the P-38's Hispano was a US manufactured gun made to US specs, it just benefited from a very rigid mount in the nose.

I've posted some reliability stats on the US Hispano here before, I'll see if I can dig them up.

 

[rinkol]

Germans, Italians and Japanese used the explosive ammo for their heavy MGs during the ww2. Is there an assesment of how good actually that type of ammo was worth it vs. a (probably) simpler and cheaper API?

Paging also A A.G. Williams

I think the muzzle velocity is something that is an issue and makes a difference. If you have a high muzzle velocity, then you can rely on the kinetic energy to result in significant effect at the target. Conversely, with a lower muzzle velocity, it becomes more worthwhile to use explosive ammunition.

Interestingly, the Germans, after experimenting with the MG 151/15 largely standardized on the 20mm version, which had a lower muzzle velocity, but could fire the so called mine shells.

 

[Shortround6]

I think the muzzle velocity is something that is an issue and makes a difference. If you have a high muzzle velocity, then you can rely on the kinetic energy to result in significant effect at the target. Conversely, with a lower muzzle velocity, it becomes more worthwhile to use explosive ammunition.

Interestingly, the Germans, after experimenting with the MG 151/15 largely standardized on the 20mm version, which had a lower muzzle velocity, but could fire the so called mine shells.

The 15mm was easier to hit with (required less lead) but while the 15mm HE held about 3 times the HE of the 12.7/13mm projectiles it was roughly 1/3 as much as the normal 20mm projectiles would hold. And about 1/7th what the Mine shell would hold. German 20mm shells after the MG/FF were about 10-13 grams lighter than the 'normal' 20mm projectiles and that weight came out of the middle of the shell where the thinnest walls and most explosives were.

And they sucked up a lot of space with the tracer, But then this tracer round was supposed to match the trajectory/time of flight of the Mine shell, at least at Air to Air ranges since the Mine shell could not hold tracer. Getting the tracer to explode when it hit something was sort of a bonus

This illustrates the problem with 12.7/13mm projectiles. Even in a 20mm the fuse takes up a lot of space and weight (fuses were usually brass) and if you stick a tracer compartment in the back you have even less room for the HE. And you cannot make the shell walls too thin in high veleocity shells or the shell walls tend to collapse with pressures/stress of firing.
That was the secret of the mine shell. The German company had figured out how to deep draw steel with acceptable strength and quality (if the steel got too hard from 'working' it would be too brittle and would crack.)