An endless ammunition conveyor includes a set of laterally moveable carriers and a set of laterally fixed carriers arranged in alternating relation with the moveable carriers. Incident with conveyor movement, the moveable carriers are cammed between laterally offset positions relative to the fixed carriers for respective round exchanges with a pair of ammunition storage bays and interleaved, longitudinally aligned positions with the fixed carriers for round exchanges with a gun-feeding transfer unit. Concurrently, the pitch between adjacent fixed and moveable carriers is changed between a maximum pitch at the gun end of the conveyor and a minimum pitch at the bay end of the conveyor.