One of the interesting things is that the US has effectively re-invented the 7.62x39 round (at a much higher per round cost) with same weight bullet and nearly same length, which is the .300 Blackout supersonic.
It's designed to work in a standard NATO 556 magazine, receiver and bolt carrier, the cartridge body is the same as a 556 NATO, it's necked to take a 7.62 bullet.
It's designed to work in a standard NATO 556 magazine, receiver and bolt carrier, the cartridge body is the same as a 556 NATO, it's necked to take a 7.62 bullet.
https://thebiggamehuntingblog.com/300-blackout-vs-7-62x39/