The 7.62x39 M-43 is a ballistic duplicate of the German PP-39 used in the MP-43/44/StG-44 rifles.
The Germans made it on draw dies for the 7.92x57, which they already had in stock; the Russians used the same draw as the 6.5 Jap which they had been experimenting with since 1916.
Ballistically, they were the same, propelling 122/123 grain bullets at around 2250 ft/sec.
There is very little Russian INVENTION in the ammo, although the DEVELOPMENT is brilliant.
Just a slightly-different perspective on things, I guess.
Nice video.