M203

The M203 is a single-shot, pump-action 40 mm grenade launcher designed to attach beneath a rifle barrel. It was the only element of the US Army's Special Purpose Individual Weapon programme to reach production, entering service in 1969 and reaching US forces in the early 1970s as a replacement for the M79 and the conceptually similar Colt XM148. The M79 had been a stand-alone weapon, usually the primary armament of the soldier carrying it; the M203's under-barrel layout was chosen precisely because 40 mm ammunition is heavy and bulky, limiting how much can be carried, and because a grenade is the wrong answer at close range or near friendly troops. Mounting the launcher under a rifle lets the grenadier carry both and switch instantly between them.

It fires the same 40x46mm SR low-velocity rounds as the M79, which use the high-low propulsion system to keep recoil manageable from a shoulder-fired weapon. The launcher attaches under the barrel with the trigger at the rear, just forward of the rifle magazine, and the magazine itself serves as the firing hand grip. Because the rifle's own sights are not calibrated for the grenade trajectory, a separate right-handed sighting system is added, either a leaf sight used with the front sight post or a quadrant sight mounted to a Picatinny rail or the M16 carrying handle. Aimed fire runs at 5 to 7 rounds per minute, rising to 15 to 17 for area suppression, with an effective range of 350 m against a fire-team sized area target and 150 m against a point target such as a vehicle or weapon position.

The round selection is what gives the weapon its versatility. The M433 high-explosive dual-purpose round penetrates at least 5 cm of steel armour at 150 m and has a 5 m kill radius with casualties out to 130 m; the M406 is the plain high-explosive equivalent. Beyond these there are the M583A1 star parachute and M585 white star cluster illumination and signalling rounds, the M713 ground marker, the M781 practice round, the M651 CS round for riot control and urban operations, and the M576 buckshot round carrying twenty pellets for thick vegetation or room clearing.

Variants differ mainly in barrel length and mounting. The original M203 has a 12-inch rifled barrel and is intended for permanent attachment to the M16A1, A2 and A3; it will not fit the M4 series unmodified. The M203A1 uses a 12-inch barrel with a bracket mount for the M4 and M4A1, while the SOPMOD M203A1 has a 9-inch barrel. The M203A2 pairs a 12-inch barrel with a quick-release bracket for the M4 series and M16A4 alongside the Knight's Armament M5 rail system. Colt Canada's M203A1 uses a different mounting system whose barrel slides further forward, allowing longer rounds. The M203PI kit adapts the launcher to other host weapons including the Steyr AUG, the G3 and the MP5. The M320 is replacing the M203 in US Army service, offering a day/night sight, a double-action trigger and a side-loading breech; the Marine Corps began issuing it in June 2017, while the Air Force, Coast Guard and Navy retained the older launcher.