"To the People's Commissar of Ammunition of the USSR, comrade Vannikov
Chief of the Red Army GAU, comrade Yakovlev
Deputy Chief of Armoured and Motorized Vehicles of the Red Army, comrade Korobkov
In accordance with GOKO decree #6868s issued on February 4th, 1944, the People's Commissar of Tank Production instructed the Kirov factory to study the issue of single piece ammunition for the 122 mm D-25 gun.
Dummy rounds were produced at the Kirov factory according to blueprints developed by the People's Commissariat of Armament. The ability to load the gun as well as placement of the rounds in the fighting compartment of the tank and SPG was tested.
The results of the test showed that:
- It is impossible to load the D-25 gun in the IS-2 tank with the current sized round at any angle. In many cases the gun could be loaded at a certain angle if the turret bustle is emptied of ammunition.
- The IS-2 tank can fit only 12 rounds.
- The ISU-122-2 can fit 25 rounds.
- In the ISU-122-2 SPG if the gun is aimed to the right it is impossible to use ammunition from the rack on the left of the fighting compartment and vice versa.
All performed work was recorded by a commision that included representatives of the GBTU and GAU.
The Kirov factory concludes that satisfactory use of single piece ammunition with the D-25 gun would be possible only if the complete round is no more than 1000 mm long.
People's Commissar of Tank Production, V. Malyshev"
This entry proved some thoughts, which I know. As example- I have found thought that two-piece ammunition can be better than one-pieco ammo, if we want big number of ammo in tank. This situation exist, because this space of a tank which is too small for put one-piece cartridge, can be good enought for put projectile or case with propellant. As example, in American M26E1 we have 41 one-piece cartridges for gun, in T26E4 we have 54 two-piece cartridges for gun. Also, I have found opinion that typically maximum accaptable lenght of one-piece cartridge in a tank that's around 100 cm (and around 25 kg of weight). BTW- western heavy tanks from early stage of cold war (M103 and Conqueror) also use two-piece ammunition (Chieftain and Challenger MBTs too). Of course, Leopard 2 use one-piece ammunition, but I have found opinion that German designers of 120 mm gun have big emphasis on small size and small weight of ammunition. As example, due usage powerfull propellant, 120 mm cartidge case still can be pretty small and pretty light. Also, probably APFSDS or HEAT projectile is lighter than WWII classic full caliber AP or HE projectile. Generally, technology which exist in Germany in 70ties, don't must exist in Soviet Union of 40ties (probably Soviets can't build small and light 122 mm one-piece cartridge for IS-2 tank).
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