"Penetration trials
Penetration trials were conducted in parallel with a 20 mm ShVAK gun and 12.7 DShK machine gun. against 20 mm thick cemented and homogeneous armour installed at normal and at 30 degrees.
The characteristics of the plates are listed in attachment 6.
Firing was done with the following types of ammunition:
- 20 mm B-3, P-85, factory #187, 1941 production, VTUF 1/41 K propellant.
- 20 mm NB-200, reloaded by NII-6, 1941 production.
- 12.7 mm B-32, P-1, U-1941, 4/7 FL 9/40 RUF
- 12.7 mm B-30, D-16-3, 1940, SV-7/39 R
The results of trials are shown in the table (attachment 7). The following conclusions can be drawn:
- The 20 mm AP-I round cannot penetrate a 20 mm cemented plate at 135 m either at 30 degrees or at normal.The same round doesn't penetrate a homogeneous plate installed at 30 degrees from 135 m. A homogeneous plate installed at normal was penetrated at a range of up to 400 m inclusive.
- The 20 mm AP-I NB-200 (increased muzzle velocity) round does not penetrate a 20 mm cemented plate installed at 30 degrees or at normal at 135 m and does not penetrate a 20 mm homogeneous plate installed at 30 degrees from the same distance.The same round guarantees 100% penetration of a 20 mm thick homogeneous plate at normal at ranges of up to 500 m inclusive.
12.7 mm DShK machine gun
- The 12.7 mm B-30 bullet does not penetrate 20 mm homogeneous or cemented plates installed at 30 degrees from 135 m.
- The 12.7 mm B-32 bullet has a 20% chance of penetrating a 20 mm cemented plate installed at normal from 135 m.
- The 12.7 mm B-32 bullet has about a 50% chance of penetrating a 20 mm homogeneous plate installed at normal up to a range of 400 m inclusive.
From this data we see that the penetration of the 20 mm ShVAK gun against 20 mm thick cemented or homogeneous armour installed at an angle of 30 degrees is equivalent to that of the 12.7 mm machine gun (no penetration).
Against a 20 mm homogeneous plate installed at normal the ShVAK has a small advantage in the form of a larger distance at which 100% penetration is achieved."
This appears to be an early part of the same trials the conclusions of which I posted earlier, which indicate that the guns had slightly more success against 15 mm thick cemented armour (penetration at 30 degrees could be achieved from 100 m).