M129 grenade launcher

The M129 was a 40 mm automatic grenade launcher used as an aircraft weapon in United States service. It was developed from the earlier M75 as a redesign that put the barrel concentric with the operating drum, which removed the torque that troubled the M75, and it raised the rate of fire to as much as 400 rounds per minute against 225 for the M75. A special feed tray let it fire both the high-velocity 40x53 mm grenade and the lower-velocity 40x46 mm grenade, and it could switch at once between electric operation and a manual hand crank. It was fitted to the chin-mounted M28 series armament subsystem of AH-1 Cobra helicopters and was also used on the UH-1H, OH-6A and OH-58 light helicopters and the AH-56 Cheyenne.