The M203 is a single-shot, pump action, 40 mm under-barrel grenade launcher designed to attach to a rifle. It uses the same rounds as the older stand-alone M79 break-action grenade launcher, which utilizes the high-low propulsion system to keep recoil forces low. While compatible with many weapons, the M203 was originally designed and produced by the United States military for the M16 rifle and its carbine variant, the M4. The launcher can also be mounted onto a C7, a Canadian version of the M16 rifle; this requires the prior removal of the bottom handguard.