Abstract: An apparatus for converting an automatic firearm of high caliber including a frame, a receiver mounted on the frame, a barrel mounted on the receiver, a bolt disposed on the receiver telescopically moveable relative to the breech end of the barrel against the action of a recoil spring, and the bolt being controlled by a sear which is movable in response to the movement of the weapon trigger and a disconnect lever, to a low caliber automatic firearm is disclosed. The apparatus for conversion includes a frame disposed in the receiver of the firearm, a low mass bolt assembly including a bolt carrier, a bolt, and a sear foot disposed in sliding contact with the frame. A pivotable camming lever is attached to the frame and pivots in response to impact from the bolt carrier. The camming lever provides sufficient mechanical advantage to enable the forward impact of the low mass bolt assembly to depress the disconnect lever on the original weapon.