A recoil-operated, impulse averaging, air-cooled, magazine-fed, automatic weapon. An operating group of the weapon includes a chamber, a bolt, a barrel extension and one or more toggles. The recoil action of the weapon from firing a first round drives the toggles in a motion constrained by a cam way. The toggles then drive the chamber in a linear reciprocating motion ejecting a first round and over-riding the next round. An impulse averaging system controls the speed of the recoil.