The pre-74 AKs fired a full-caliber, but half-length, intermediate cartridge, the 7.62x39mm. This was easier to manufacture on existing pistol round tooling tha

The pre-74 AKs fired a full-caliber, but half-length, intermediate cartridge, the 7.62x39mm. This was easier to manufacture on existing pistol round tooling than a SCHV round. The 7.62mm NATO cartridge you're thinking of is 7.62x51mm, and fires a 25% heavier bullet at 18% higher velocity, for 66% more total kinetic energy than the early AK round. And the Soviet full-power round that the 7.62x39 replaced, the 7.62x54mmR, is even larger. https://en.m.wikipedia.org/wiki/7.62×39mm https://en.m.wikipedia.org/wiki/7.62×39mm https://en.m.wikipedia.org/wiki/7.62×51mm_NATO https://en.m.wikipedia.org/wiki/7.62×51mm_NATO