CAMD RF 81-12040-276
"As can be seen from attached results, doubling the length of the barrel (from 250 mm to 500 mm) increases the Parabellum bullet's speed from 396 to 409 m/s, or by 9-17 m/s, and changing the cartridge gives an average increase of another 5 m/s.
It can be concluded that increasing the power of a Parabellum round by slightly modifying it for the 39.M autocarbine was not achieved.
The lengthening of the barrel gave another almost negligible increase in speed (13 m/s on average), which indicates that the solution is ineffective and a barrel length of 500 mm is excessive.
The 39.M round cannot be considered a high power pistol round at all, as it is weaker than some pistol rounds, like the American 7.62 mm self-loading M-1 carbine.
For example, the 39.M round is less powerful than the domestic pistol round, as with an equivalent barrel length (55-56 calibers), the 39.M barrel provides the bullet with 72.3 kgm of energy, while the domestic pistol bullet achieves 87.0 kgm, or 20.03% greater.
Overall data on the 39.M carbine
The 39.M carbine is an automatic weapon that works on the principle of bolt recoil.
Photo #3. Overall view of the 39.M carbine (with a bayonet and collapsed magazine)."