Alternative light and anti-tank guns, 1935-45

[Shortround6]

What the Germans do not need is a small batch of guns using oddball ammo that need either totally new carriages (keep barrel and Breechblock) or large tractors to move.

Leave them in France and use them as AA guns.

 

[tomo pauk]

What the Germans do not need is a small batch of guns using oddball ammo that need either totally new carriages (keep barrel and Breechblock) or large tractors to move.
Leave them in France and use them as AA guns.

Germans did went through the trouble with the French 75 installed on the new carriages, despite the sedate AP performance. Or they can avoid the need for the new carriage and use it as the sharp end of an SP AT vehicle.
They can have the ammo manufactured for their needs, and can also give the pak 36(r) treatment to these guns.
Another option is to modify the barrel for the 7.5cm 1916 n.a. ammo to be used on these guns.

 

[Shortround6]

Germans 'converted' 3,712 (?) guns to Pak 1897/38 configuration and often used 5cm Pak 38 carriages to do it.
Pak 1897/38 also use captured French/Polish ammo for the HE rounds and they also used captured Polish AP rounds.
They used German hollow charge rounds in French cases and propelling charges.
There were problems with the Pac 38 carriages, even with the muzzle brake the guns tended to be unstable and the carriages broke more often under repeated firing than the Pak 38s.

Coming up with a conversion scheme for 200 barrels and having to adopt a different carriage and or cartridge to do it?
A lot of effort for not much result.

 

[tomo pauk]

Germans 'converted' 3,712 (?) guns to Pak 1897/38 configuration and often used 5cm Pak 38 carriages to do it.
Pak 1897/38 also use captured French/Polish ammo for the HE rounds and they also used captured Polish AP rounds.
They used German hollow charge rounds in French cases and propelling charges.
There were problems with the Pac 38 carriages, even with the muzzle brake the guns tended to be unstable and the carriages broke more often under repeated firing than the Pak 38s.

Carriage from the pak 38 will certainly not do it in this case.

Coming up with a conversion scheme for 200 barrels and having to adopt a different carriage and or cartridge to do it?
A lot of effort for not much result.

See it from the German perspective.
Apart from the 8,8s - whatever the token number the LW was willing to release from the 'West' - and the pak 38s with APCR shots (= need tungsten), there was almost nothing to reliably tackle the new Soviet tanks in the 1st 8 months of the war in the East. Extra 200 guns that can deal with these tanks and can be added to that force would've been more than nice to have. Yes, some forethought will be required for these guns to be deployed against the Soviets as early as possible.

Or, ship them to the N. Africa.

 

[Shortround6]

Without a new carriage the existing carriages went about 4100-4200kg emplaced. For transport they were well over 5000kg.
There is just too much that needed changing for too few guns. Some sources say they had 6 power scoped available but no AP ammo?
First few month the Germans had trouble with Soviet tanks but they were somewhat able to get around them.
Without modifications the French 75mm AA guns weren't much better than the Soviet 76mm field guns, around 25ms more velocity?
The Soviet guns were already in Russia, they had AP ammo (at least some) they needed few horses or lighter trucks to tow them.

If you want to start rebuilding something, find something that had a larger base stock to work with.
I have no idea why the French needed a 561mm long case for just 700-715mps velocity. Error? Or using different propellent?

 

[marathag]

Perhaps some 850 m/s would've been achievable with the 'cheapo APCR'?

US had tested the T45, a HVAP for the M3 75mm gun.
8.4 lbs/3.8kg projectile at 2870fps/870m/s
116mm penetration at 500 yard with 30 degree plate

Not produced: decided that the HVAP for the TDs was more important.

Considering the TD fired more HE than AP during the War, this was a bad call. One or two HVAP for each M4 would have been a morale booster.

 

[Elan Vital]

If you want to start rebuilding something, find something that had a larger base stock to work with.
I have no idea why the French needed a 561mm long case for just 700-715mps velocity. Error? Or using different propellent?

The 75mm SA 44 tank gun using the same ammunition as the AA guns used 1270g of BG5 propellant at 2400 kg/cm² pressure to shoot at 715 m/s, while the 76mm M1 apparently used 1700g (3.75 pounds) of propellant at a chamber pressure of 43k psi or 3000 kg/cm². I suspect that the French were just using more conservative loading for the mle.1928 type barrels and could have got more if they wanted. The case was 518mm long. Another example is the 3" M7 gun using a 1920s/30s barrel which offered the same velocity as the M1 using a greater powder charge (4.87 lbs), reduced pressure (38k psi), and lower proportion of case volume filled with propellant.

During overspeed acceptance tests, the loading was 1330g at 2600 kg/cm², and for overpressure tests, they used BSP propellant and reached 2900+-100 kg/cm².

For the 75 mle.97 pattern, in a document related to development of the fortification assault tanks and their armor, it had been stated "the maximum muzzle velocity achievable in a gun with the interior dimensions of the 75mm mle 97 with a projectile of 6.4 kg (under certain conditions). My interpretation is they meant a gun with the same chamber dimensions (same case), but adapted loading and either the same or a longer barrel much like the 75mm M3 with barely lower velocity, while retaining acceptable barrel life. This 640 m/s gun had been approved for the fortification assault tank before going to the 90mm later on.

They got to test a new 75mm capped AP projectile, which perforated a 95mm cemented plate from the Thüringen battleship at 20°, and even 25° for half the shots, at 640m/s (1).
Against a 100mm Schneider naval quality RHA plate, it perforated at 20°, but not at 25° (half-plate deep penetration).
Against 120mm naval quality cemented plate at 0°, it was at the limit of back plate integrity (one spall).
Against 120mm RHA, it only made a 135mm deep dent with a bulge.
75mm mle.1910 couldn't penetrate 100mm plate at all.

Later on, modern uncapped AP analogous to the capped round (same metal as well) achieved back plate integrity limit (light spall) on 120mm RHA under the same conditions, showing the merits of capped and uncapped ammo against cemented and RHA plates. (2)

This is how they settled on 120mm thick cemented plate so that the tank could be safe against uncapped 75mm ammo in similar conditions with "War" rather than naval type plate. The previous 100mm requirement was against the 47mm casemate/mle 37 gun, with 105-110mm actually being preferable to be at full immunity even against back plate damage.

(1) actually lowered by 5 m/s due to the slightly heavier projectile, to keep the same striking energy
(2) velocity increased by 10 m/s due to the lighter round, to keep the same striking energy

I regret not taking pictures of it for later, but one of the archive documents I found was talking about French artillery development and namely what they wanted out of the 75mm replacement before the TAZ 39 happened. For the barrel, they wanted a new quick-change barrel that would be somewhat lighter, would have greater barrel life and would be approved for higher velocities when using AP ammo.

French antitank research in 1939-40 was otherwise concerned with testing articulated self-propelled 75mm mle.1908 (850 m/s) and 90mm AT guns as a hedge against further armor increases, 47 and 75mm self-propelled mounts; a towed version of the 37mm casemate gun (2pdr/37mm M3 level) to replace the 25mm gun in 1941; and a lightweight weapon to assist the most forward echelons of the infantry (many ideas, either an extra-light 25mm AT gun that could be dismantled in a few portable parts, a 20/16mm squeezebore gun, Boys ATR as stopgap).

 

[tomo pauk]

For the 75 mle.97 pattern, in a document related to development of the fortification assault tanks and their armor, it had been stated "the maximum muzzle velocity achievable in a gun with the interior dimensions of the 75mm mle 97 with a projectile of 6.4 kg (under certain conditions). My interpretation is they meant a gun with the same chamber dimensions (same case), but adapted loading and either the same or a longer barrel much like the 75mm M3 with barely lower velocity, while retaining acceptable barrel life. This 640 m/s gun had been approved for the fortification assault tank before going to the 90mm later on.

Just to be 100% sure - the report says that 640 m/s is the maximum that can be expected from the gun that is the equivalent of the Mle.97?

They got to test a new 75mm capped AP projectile, which perforated a 95mm cemented plate from the Thüringen battleship at 20°, and even 25° for half the shots, at 640m/s (1).
Against a 100mm Schneider naval quality RHA plate, it perforated at 20°, but not at 25° (half-plate deep penetration).
Against 120mm naval quality cemented plate at 0°, it was at the limit of back plate integrity (one spall).
Against 120mm RHA, it only made a 135mm deep dent with a bulge.

What distances are in the question in these examples? When were the tests being made?

75mm mle.1910 couldn't penetrate 100mm plate at all.

Care to elaborate a bit about that gun?

 

[tomo pauk]

If you want to start rebuilding something, find something that had a larger base stock to work with.
I have no idea why the French needed a 561mm long case for just 700-715mps velocity. Error? Or using different propellent?

Seems like the French 75mm guns were too conservatively loaded, IOW, the propellant charge of under 1300 g for the AA guns. Or, half of the propellant charge weight of what the 7.5cm kwk had on the Pz-IVG and the like.

The French Navy guns (including the 75mm types) were much hotter loaded than the Army guns, even the old types.

There is just too much that needed changing for too few guns. Some sources say they had 6 power scoped available but no AP ammo?

The Soviet guns were already in Russia, they had AP ammo (at least some) they needed few horses or lighter trucks to tow them.

AP ammo problem should've been trivial to solve, involving removal of the HE shell and retrofit of an AP shot back to the cartridge.
If the guns receive a total makeover, bringing them to the pak 36(r) standard, that makes them even more worthy of consideration. I'd suggestion again an alternative to the shipping of the French guns to the East - ship them to the N. Africa.

 

[Elan Vital]

Just to be 100% sure - the report says that 640 m/s is the maximum that can be expected from the gun that is the equivalent of the Mle.97?


What distances are in the question in these examples? When were the tests being made?



Care to elaborate a bit about that gun?

Yes, an equivalent to the mle.97 at least in interior dimensions. Unfortunately the annex which discussed all this didn't say what conditions had to be met for that muzzle velocity.

All of the firing tests here are at the muzzle. The document itself dates to late 1938 (August/October). I have other documents about a new War type projectile in development by the Cail steelworks in 1937/38 with somewhat different firing trials, which was an APC with a smaller HE cavity than the previous round and generally much more modern steel and hardness pattern. It has been alleged by French historians that the final APC/APCBC projectile adopted in 1940 was a design from the Firminy steelworks. In any case, similar trends.

Forgive for my wording: the mle.1910 is not a gun, but the standard AP shell in service in the French Army at the time for the 75. Old naval APHE with no cap and a very big HE cavity.

 

[Juha3]

Sifting through some web resources, the 'Jaegerplatoon' website gives some interesting data for the Soviet 76mm AA gun firing the Finnish-made APC shot at 20 deg sloped armor (or 70 deg, depending on what side of the pond one is ). Supposedly at 1000m it was able to pierce 125mm (almost 50% more than the Pak 40 against the 30 deg sloped plate) - IOW the Tiger I tank is a fair game at that distance. Or, barely worse than the Tiger's gun at the same distance??
J Juha3 - help

Hi Tomo
I agree with Bf109xxl, something strange in the table or target plates have been substandard.
I tried to find more info from some of my books, it didn't help, the book about the coast artillery's cannons, Itsenäinen Suomen Rannikkotykit 1918-1998 by Ove Enqvist, mentions anti-tank ammunition and according to the book, Finns got plenty of them along with the 72 cannons that the coast artillery got from Germany in 1944. But understandably, it doesn't mention anything of penetration, the main use of these cannons in the coastal artillery was AA.
The AA cannon book, Itsenäinen Suomen Ilmatorjuntatykit 1917-2000 by Vehviläinen, Lappi and Palokangas, of course mentions the cannon, but does not mention the A/T ammo. AA units got 46 of these, all captured by the Finns.
I couldn't find any mention of 76 ItK/31 ss or 76 ItK/31-40 ss in the book about Finnish anti-tank warfare, Marskin Panssarintuhoojat by Erkki Käkelä.

So unfortunately I can't be of any help
Juha

 

[tomo pauk]

Some armor-piercing data for the 30mm AA gun M53/59 (the 'PZO' cartridge), that probably shared a lot with the German MK 303 project (1000 m/s, 440g shell); click to open hi-res:



PZO means here 'API-T', the inciendary mixture (item 2) was located in the front of the shot, 'surrounded' by the cap. Note the core, but that was probably just the hardened steel, the manual for the ammo does not brag about the core being of tungsten/wolfram. So the shot is kinda-sorta 'APCR minus'.



The 'minus' part shows - AP performance was much worse than what the MK 103 was doing with a proper APCR shot, even though the later was lighter and fired at lower MV than what the M 53/59 was doing.

 

[bf109xxl]

These guns were also to shoot the tungsten-cored ammo, again pointing out that their opinion on the steel-cored ammo was very different to yours.

I'm still studying armor penetration - trying to understand how much the caliber of the projectile mattered, and how much the design of the projectile mattered for different types of armor and different thickness. Soviets used homogeneous armor of high (or very) hardness, even late cast Soviet armor was high hardness, Germans used heterogeneous armor (with rare exceptions at the end of the war), Americans used medium to low hardness armor with a high proportion of cast parts, etc. In some cases APCR was optimal, somewhere only a high hardness cap was sufficient. In addition to armor properties, the ratio of core size and armor thickness mattered. All this is time-consuming, but I still want to get some kind of overview for myself.
Some of the things that came across during my research: scans of Soviet reports (terrible quality, unfortunately) on tests in early 1942 of 45mm APCR with different core materials and different projectile design, but the same geometry for each core material (tungsten carbide or high-hardness steel). It turned out that I was wrong: steel cores demonstrated much worse armor penetration and were never mass-produced - they were even banned from further testing.
A projectile with a more massive core had higher armor penetration but worse accuracy and was rejected.
When German shells were fired from a Soviet 37mm anti-tank gun in 1941, the armor penetration was superior not only to the original Soviet shells but also to that of Soviet 45mm shells.

 

[marathag]

I'm still studying armor penetration - trying to understand how much the caliber of the projectile mattered, and how much the design of the projectile mattered for different types of armor and different thickness.

spend some time here, if you haven't already
Nathan Okun Naval Gun and Armor Data Resource - NavWeaps

 

[bf109xxl]

spend some time here, if you haven't already
Nathan Okun Naval Gun and Armor Data Resource - NavWeaps

Thank you! I read the site about 15-20 years ago, probably if I'm not mistaken.
Unfortunately now I'm more interested in information that I can hardly find there.
For example, penetration is not necessarily to hit a tank armored with very high hardness armor (i.e. Soviet tanks). It turned out that even just when the projectile impacts the armor a flux of secondary fragments from the inner side of the plate was generated, hitting the crew and equipment in the armored volume.

 

[marathag]

Thank you! I read the site about 15-20 years ago, probably if I'm not mistaken.
Unfortunately now I'm more interested in information that I can hardly find there.
For example, penetration is not necessarily to hit a tank armored with very high hardness armor (i.e. Soviet tanks). It turned out that even just when the projectile impacts the armor a flux of secondary fragments from the inner side of the plate was generated, hitting the crew and equipment in the armored volume.

Spalling is the tradeoff for very high hardness armor. one of the reasons why the UK used HESH so much
Everything is a tradeoff.

 

[bf109xxl]

Spalling is the tradeoff for very high hardness armor. one of the reasons why the UK used HESH so much

But the Germans used heterogeneous armor with a medium hardness backside, and the Soviets used medium hardness armor (42SM, 52S) after the war.

 

[tomo pauk]

A few posts ago in this thread, I've suggested that the small gas divert tube is added to the small AT gun so the recoil is lowered, since part of the high-speed gasses is pushed backwards. That again means that the whole gun can be lighter due to the lower stress exerted on the weapon. Sorta 10% recoiless gun.
That principle was used on the Croatian RT-20 anti-material rifle, that went under 20 kg despite using the high-power 20mm Hispano cartridge. For comparison, the Solothurn S18-100, that used a lower-powered 'short Solothurn' cartridge, went to 40 kg.
See here the short video of the RT-20 firing (somewhere in Croatia?), with the gunner uttering some cuss

 

[bf109xxl]

A few posts ago in this thread, I've suggested that the small gas divert tube is added to the small AT gun so the recoil is lowered, since part of the high-speed gasses is pushed backwards. That again means that the whole gun can be lighter due to the lower stress exerted on the weapon. Sorta 10% recoiless gun.

Why go to all that trouble when you can just reduce the charge? Just increased powder consumption.

 

[tomo pauk]

Why go to all that trouble when you can just reduce the charge? Just increased powder consumption.

Quirk with this system is that one still uses the off-the-shelf ammo.
RT-20 was supposedly doing 850 m/s, despite the short barrel and the divertion of small % of the gasses.