A cartridge feeder for a gun having two alternately fired barrels has respective adjacent loading positions. The feeder comprises a guide defining a path having an upstream end and a downstream end, the latter being at one of the positions and the other position being between the downstream and the upstream end. Cartridges are movable in a row along the path and are laterally displaceable out of the path at the positions, so they can be chambered directly from this path. A sprocket at an upstream end of the path is rotated while in engagement with a sequence of cartridges to advance same into the upstream end and thereby push the cartridges along the path into the positions. The feeder can be formed in part by an endless flexible conveyor having a stretch extending along the path opposite the barrels and formed with a succession of cartridge-engaging holders. It can also be closed at its downstream end and provided with a pawl that blocks cartridges from moving backward along the path in the guide from the downstream to the upstream end.