GABTU Chief, Lieutenant-General of the Tank Forces, comrade Fedorenko
On the issue of installing the ZIS-6 into the KV-3 tank
We accompany the design for installing the ZIS-6 gun into the KV-3 tank with the following characteristics:
- Muzzle velocity: 800 m/s
- Recoil resistance: 20,000 kg
- Mass of the recoiling parts: 1600 kg
- Mass of the oscillating part with the gun mantlet: 2600 kg
- Recoil length: 640 +/- 40 mm
- Ammunition: one piece
- Breech: semiautomatic
- Coaxial DT machinegun
- The horizontal range of the gun is from +20 degrees to - 5 degrees.
- The recoil mechanisms allow firing from +40 degrees to -15 degrees.
- The gun will have a fume extractor.
- The length of a shell casing is 625 mm.
- The length of the full round (HE) is about 1200 mm.
- The initial pressure in the recoil brake is 50 atm.
- The TD telescopic sight is installed.
- The armour layout will be of the same type as in existing KV turrets.
- The experimental prototype of the gun will be tested in the KV-2 tank turret.
Factory #92 is completing the design of the ZIS-6 gun, but nevertheless complaints made by your designers will be remedied, since the system will be reworked. At the same time, some complaints cannot be remedied, as their solution falls under the jurisdiction of your factory (the frame and armour protection are not within our scope).
The request to replace the one piece round with a two piece round is a revision of the Party and Government's decision, which factory #92 cannot do. At the same time, factory #92 did everything possible to ease the loading of a single piece round and designed the gun to have the minimum possible dimensions.
To resolve the issue of two piece ammunition, contact the appropriate authorities.
Chief Designer (Grabin)
April 20th, 1941"