Wednesday, 17 February 2016

45 mm Gun Upgrade

"February 27th, 1942
To the Chair of the Artillery Committee, Major General of Artillery Hohlov

RE: Modernization of the 45 mm mod. 1937 anti-tank gun

Considering the importance of this task, Molotov factory #172 immediately began the modernization of the 45 mm mod. 1937 AT gun according to specifications in letter #567079 sent on February 4th, 1942.

The modernizations proposed by the factory based on the requirements attached to letter #567079  are as follows:
  1. Monobloc barrel from OHNZM type steel with a robustness category of 0-70, barrel length of 2855 mm (63.5 calibers), muzzle velocity of 880 m/s, maximum chamber pressure of 3075 kg/cm^2, propellant density of 0.75, and minimum chamber robustness reserve of 1.25.
    The breech and semi-automatic mechanisms are unchanged.
  2. The upper and lower mounts are changed slightly in connection with the changes made to the screw type turning mechanism.
  3. The recoil brake is unchanged. The trails remain unchanged as well.
Currently, blueprints for the barrel, breech block, and breech are ready and the parts are being machined. According to the factory schedule, trials will start on April 1st of this year.

At the same time as this modernization work is being done, the NKVD Special Design Bureau is working on a modernization design that only replaces the barrel, keeping the existing breech block and semiautomatic mechanisms, with the aim of being able to replace the barrels on already existing gun mounts.

The NKVD 45 mm mod. 1937 AT gun modernization project is as follows:
  • Increase of the barrel length by 27.5 calibers compared to the existing length.
  • Robustness category of 0-80.
  • Increase of the gunpowder charge by 35 grams.
  • Maximum chamber pressure of 3100 kg/cm^2.
  • Propellant density of 0.76.
  • Minimum robustness reserve of 1.18.
  • Muzzle velocity of 920 m/s.
  • Penetration of 54 mm of K=2400 armour at 30 degrees at a range of 400 meters.
Due to the lengthening of the barrel by 27.5 calibers, the center of gravity is moved by 150 mm and the breech is made heavier to compensate for this unbalance. In order to maintain connection to the semiautomatic mechanism, which is not altered or moved, the semiautomatic rod (part 02-43) is lengthened to the necessary size.

Due to the change in the center of gravity, the maximum gun elevation is reduced from 25 degrees to 21 degrees 40 minutes. 

Factory trials of the NKVD variant are planned for March 10th of this year.

Comparing the two variants, the second variant provides a quick solution for the issue of increasing the strength of our gun. Connecting this issue to production numbers, the Molotov factory variant promises to reduce the amount of machinery hours from 550 to 250 per unit (according to preliminary calculations) due to a modernized mount. 

The overall issue, increasing power and increasing the amount of units built, is better solved by using the NKVD barrel and Molotov factory mount.

I ask for further directions and the schedule of factory trials.

Senior UVNA Military Representative, Abramov
UVNA Military Representative, Sharonov."

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