ZiS-5

"In order to solve the issue of arming the KV-1 tank manufactured by the Chelyabinsk Tractor Factory, the workers of factory #92, factory director comrade Elyan, chief engineer comrade Grabin, and chief of the OGK sub-department comrade Muravyev, determined the following:

1. In August of this year, factory #92, while mounting the F-34 gun on the KV-1, reinforced the gun mount as a result of having to move the trunnions in order to balance the gun (which takes as much effort as making a new mount).
2. The resulting 76.2 mm caliber gun is called "ZiS-5" by the factory, and is preferable for installation in the KV-1 tank for the following reasons:
1. The mount is sturdier, with 15 mm walls instead of 8 mm.
2. The button firing mechanism is made according to the Artkom GAU KA journals, and is superior in performance. 
3. A T-900 4x sight is used instead of a 2.5x sight, in order to reduce the opening in the gun mantlet.
4. The muzzle velocity of the armour piercing shell can be increased to 780 m/s with a special charge, which increases penetration to 75 mm at 1000 meters.
3. Factory #92 received an order from Moscow to cease manufacturing of prototypes, despite the fact that parts for 25 prototypes have already been produced.
4. Since the Kirov factory has stopped supplying ChTZ with F-32 guns as of August this year, ChTZ was ordered to install the F-34 gun on the KV-1, with all required mount trunnion changes. In order to assist in this, one engineer from factory #92 was sent to ChTZ by airplane with one F-34 gun, and later, 16 more F-34 guns were sent by rail. If necessary, factory #92 can send more of its employees.

Conclusions:

1. It will take as much time to adapt the F-34 gun to the KV-1 as it would take to produce the ZiS-5 gun.
2. No additional equipment is required to produce the ZiS-5 gun. Required tools have already been ordered by the factory. The factory has necessary blueprints and instruments.
3. Factory #92 can start manufacturing ZiS-5 guns at the cost of removing other guns from production, such as the F-34.
4. Major-General comrade Grabin made it clear that he can produce 20-25 ZiS-5 guns in excess of the factory's quota.
5. Major-General comrade Grabin stated that all he saw on the issue of producing the ZiS-5 is talk, and despite its advantages, there is no singular decision. If this continues, he will have to write to Stalin personally.

September 27th, 1941"

CAMD RF 38-11355-148

Letters to Stalin or not, but the ZiS-5 gun made it into mass production for the KV-1. The special AP shell, on the other hand, didn't, as every source that I have read gives identical ballistics for the F-34 and ZiS-5.