the barrel, bolt face, and gas piston, then oil lightly and reassemble. [21] Ballistics Main article: 7.62x39mm The standard AK-47 or AKM fires the 7.62x39mm cartridge with a muzzle velocity of 710 metres per second (2,300 ft/s). Muzzle energy is 2,010 joules (1,480 ft·lbf). Cartridge case length is 38.6 millimetres (1.52