General Electric , Dillon Aero INC , DeGroat Tactical Armaments, Garwood Industries Produced 1962-present Variants See text Specifications Length 801 mm Barrel length 559 mm Cartridge 7.62x51mm NATO Caliber 7.62 mm (0.308 in) Action Electrically driven rotary breech Rate of fire Variable, 4,000 RPM (practical maximum)/ 6,000 RPM in some applications