Abstract: An automatic firearm and particularly a gas operated weapon comprises a cartridge feeding system which operates upon movement of a reciprocating breech block during recoil and counter recoil to feed a series of cartridges in succession to the cartridge chamber of the gun barrel under the control of gas pressure which is generated during the firing of each cartridge. The cartridge feeding mechanism includes a drive head having a rotatable bushing which is driven by a gear drive and with an end drive face which has an engagement slot therein formed with inwardly tapering walls in a direction inwardly of the drive face. A cartridge feed mechanism is pivoted to the drive head and it may be positioned in engagement with the drive head or removed for purposes of changing ammunition. The cartridge feed mechanism includes a drive hub with a transfer element in said hub which has an outwardly tapered couplng portion which is engageable in the slot of the drive face of the rotatable bushing.