M16 rifle with M203 40mm Grenade launcher

The M203 is a single shot 40 mm grenade launcher that attaches to a number of popular assault rifles, but was originally designed for the U.S. M16 and its variant, the M4 Carbine. In the U.S. military, when a rifle or carbine is equipped with the launcher, both weapons are collectively referred to as an M203. The launcher can also be mounted onto a C7, a Canadian version of the M16 that uses an optical scope instead of an iron sight. Stand-alone variants exist as do versions capable of being used on many other rifles. The device attaches under the barrel and forward of the magazine, the trigger being just forward of the rifle magazine. The rifle magazine functions as a hand grip when firing the M203. A separate sighting system is added to rifles fitted with the M203, as the rifle's standard sights are not matched to the launcher.