Alternative light and anti-tank guns, 1935-45 (1 Viewer)

[tomo pauk]

The topic of making the most out of a medium velocity 75 pops up again, with several options for 75mm kan m/41 involving 5 or 10 caliber longer barrels, a new propellant load within the same case or a combination of both. OG gun shoots a 6.3kg proj at 590 m/s, between 75 M2/Mle 97 and M3. Hot load takes it straight to 625 m/s. 5 cal extension adds 25 m/s and 10 cal 50 m/s. The kan m/41 can be brought to French 75 640 m/s class or to an intermediate between 640 and 700 m/s class.

Americans during the ww2 were making the longer-barreled versions of their 75mm guns, that ended up on the Shermans. The increased MV by ~45 m/s gotten them about 10% of penetration. Soviet did the same for the guns of their tanks, reverting to the AP performance of the ZiS-3 gun.
One of the results was that penetration at 1000m was same as it was before at 500m with the shorter barrel.

Obviously, upping the OG French 75mm would've followed the suit here, and I'd suggest the hot-loading the charge ASAP, indeed as what the Swedes were calculating. My even more cunning plan would've been that the French go with the 'baby Pak 36' idea - upgrading the 75mm to fire the AA ammo, that went to 700+ m/s.

 

[Elan Vital]

Lurking at the Swedish archives now, aren't you
At any rate, getting to 900 m/s with a 57mm recoilles rifle is amazing.

Just re-reading the articles from the Swedish Tank Archives. There are some nice postwar articles about subcaliber ammo as well.

Americans during the ww2 were making the longer-barreled versions of their 75mm guns, that ended up on the Shermans. The increased MV by ~45 m/s gotten them about 10% of penetration. Soviet did the same for the guns of their tanks, reverting to the AP performance of the ZiS-3 gun.
One of the results was that penetration at 1000m was same as it was before at 500m with the shorter barrel.

Obviously, upping the OG French 75mm would've followed the suit here, and I'd suggest the hot-loading the charge ASAP, indeed as what the Swedes were calculating. My even more cunning plan would've been that the French go with the 'baby Pak 36' idea - upgrading the 75mm to fire the AA ammo, that went to 700+ m/s.

I think the reason they did not hot load the Mle 97 directly for full-bore ammo is that the recoil system was already close to the limit (some leeway given that the canister ammo has the greatest momentum and not AP).

Dunno if the chamber can be redone with AA cartridges. In the early 30s an AA gun firing piece was directly mounted on an arty mount. By the time it mattered the more efficient 700 m/s class firing piece was already an option.
Incidentally, I know where the plans of all (6 IIRC?) Havre/AHE 75mm field/AT gun studies from 1938-40 are, which may normally include this firing piece. Will be on my list for any future visit.

The Swedes did think about something like your proposal, mounting the patrone m/30 (of the AA gun?) on the kan m/41, but this would be too long in the tank.

 

[Shortround6]

Americans during the ww2 were making the longer-barreled versions of their 75mm guns, that ended up on the Shermans.

Yes and no, The 75mm field guns were 36 calibers in length, The US shortened the barrels to 31 calibers on the M2 tank guns, Then lengthened them to 40 calibers on the M3 guns.
Difference in performance between a 36 caliber barrel and 40 caliber barrel????

Tank guns generally needed new recoil systems, no room for the barrel and breech to move 4 1/2 feet (French 75mm) when fired.
Now not only is there R & D to be done on the recoil system, you have to figure out how to package it.
And once you have it working you have to figure out if the tank hull and turret will stand up to it. French 75 was a light gun for it's performance and it was the long recoil that allowed that. It traded long recoil travel for reduced peak recoil load.
Muzzle brakes help. But if for some reason (desired overhang?) length of tube is restricted the designer may have to decide between actual tube length and overall length.

Soviet 76mm M36 gun was already using higher performance ammo than the French 75, around 80-100ms for same weight projectile. and may have been a more suitable weapon for upgrading.

upgrading the 75mm to fire the AA ammo, that went to 700+ m/s.

The French AA guns that had 700 m/s velocity used cartridge cases 518mm long.
Maybe you can ream out the chamber?
If the case is bottlenecked you may need a new breech block.
You are going to have up grade the recoil system.

Swedes did adopt the 75mm AA gun into a tank gun in the 1950s.

26 metric tons. New turret on M/42 chassis/hull.

It was actually quite an undertaking.