The M203 is a single-shot, 40mm grenade launcher designed to attach to a rifle. It uses the same rounds as the older standalone M79 break-action grenade launcher, which utilize the High-Low Propulsion System to keep recoil forces low. Though versatile and compatible with many rifle models, the M203 was originally designed for the U.S. M16 and its variant, the M4 Carbine. The launcher can also be mounted onto a C7, a Canadian version of the M16 rifle which requires the bottom hanguard on the rifle to be removed in order to mount the launcher.
Stand-alone variants of the M203 exist, as do versions designed specifically for many other rifles. The device attaches under the barrel, the launcher trigger being in the rear of the launcher, 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. The version fitted to the Canadian C7 has a sight attached to the side of the launcher, either on the left or right depending on the user's needs.
The M203 was the only part of the army's Special Purpose Individual Weapon (SPIW) project to go into production. The M203 has been in service since 1969 and was introduced to U.S. military forces during the early 1970s, replacing the older M79 grenade launcher and the conceptually similar Cold XM148 design. However, while the M79 was a stand-alone weapon (and usually the primary weapon of troops who carried it), the M203 was designed as an under-barrel device attached to an existing rifle. Because the size and weight of the 40mm ammunition limits the quantities that can be carried on patrol, and because because a grenade is often not an appropriate weapon for a given engagement (i.e. when the target is at close range or near friendly troops), an under-barrel system has the advantage of allowing its user to also carry a rifle, and to easily switch between the two.
A new grenade launcher, the M320, will eventually replace the M203 in the United States Army. The U.S. Marine Corps, Air Force, and Navy will continue to use the older M203. The M320 features an advanced day/night sight, a double-action firing mechanism (as opposed to the M203's single action) as well as other benefits such as an unobstructed side loading breech.
The M203 grenade launcher is intended to be used as close fire support against point and area targets. The round is designed to be effective at penetrating windows, blowing up doors, producing casualties in groups of enemies, destroying bunkers, and damaging or disabling soft-skinned vehicles. Its primary purpose is to engage enemies in dead space that cannot be reached by direct fire. A well-trained M203 gunner can also use hsi weapon to suppress the enemy, both from movement and sight. In addition, the M203 can be used as a crowd control weapon when equipped with the M651 Tactical CS (tear gas) grenade. The M203 is not inteded to be used against armored or heavy targets.
The M203 is able to fire a variety of different rounds for many purposes. According tho the U.S. ARMY FIELD MANUAL FM 3-22.31 40-MM GRENADE LAUNCHER, M203, there are 8 different rounds for the M203:
- M433 High-Explosive Dual Purpose Round. The HEDP round has an olive drab aluminum skirt with a steel cup attached, white markings, and a gold ogive (head of the round). It penetrates at least 5 cm (2 in) when fired straight at steel armor at 150 meters or less, or, at a point target it arms between 14 and 27 meters, causes casualties within a 130-meter radius , and has a kill radius of 5 meters.
- M406 High-Explosive Round. The HE round has an olive drab aluminum skirt with a steel projectile attached, gold markings, and a yellow ogive. It arms between 14 and 27 meters, produces a ground burst which causes casualties within a 130-meter radius, and has a kill radius of 5 meters.
- M583A1 Star Parachute Round. This round is white impact or bar alloy with black markings. It is used for illumination and signals and is lighter and more accurated than comparable handheld signal rounds. The parachute attached to the round deploys upon ejection to lower the candle at 7 feet per second . The candle burns for about 40 seconds. A raised letter on the top of the round denotes the color of the parachute.
- M585 White Star Cluster Round. This round is white impact or bar aluminum with black markings. It is used for illumination and signals and is lighter and more accurate than comparable handheld signal rounds. The individual stars burn for about 7 seconds during free fall.
- M713 Ground Marker Round. This round is light green impact aluminum with black markings. It is used for aerial identification and for marking the location of soldiers on the ground. It arms between 15 and 45 meters. If a fuse fails to function on impact, the output mixture provided in the front end of the delay casing backs up the impact feature. The color of the ogive indicates the color of the smoke.
- M781 Practice Round. Used for practice, this round is blue zinc or aluminum with white markings. It produces a yellow or orange signature on impact, arms between 14 and 27 meters, and has a danger radius of 20 meters.
- M651 CS Round. This round is gray aluminum with a green casing and black markings. Though it is a multipurpose round, it is most effective for riot control and urban operations. It arms between 10 and 30 meters and produces a white cloud of CS gas on impact.
- M576 Buckshot Round. This round is olive drab with black markings. Though it is a multipurpose round, it is most effective in thick vegetated areas for room clearing. Inside,, it has 20 metal pellets, each weighing 24 grains, with a muzzle velocity of 269 meters per second. The round has no mechanical-type fuse.
The M203 Grenade launcher system comes with a variety of components, usually including the launcher, adaptors for attachment to assault rifles, and the leaf sights (which can be used with the rifle's front sight post). M203s can also come wiht quadrant sights.
There are numerous variant of the M203 manufactured in the U.S., and throughout the world, for various applications. These vary chiefly in the lenght of the barrel, attachment type, and quick detach (QD) capability.
The standard M203 is intended for permanent (armorer level) attachment to the M16A1, M16A2, and M16A3 rifles, and utilizes a 12 inch rifled barrel. These can also be attached to M4 and M4A1 carbines, using a different front attachment point forward of the front sight block, but the SOPMOD kit uses M203A1 grenade launchers.
The American M203A1 is intended for use with the M4 and M4A1 Carbine. The barrel is shortened to 9 inches, and principally the M203A1 QD is able to quickly detach from the rifle, and be replaced by a Knight's Armament Company M4 Rail Adapter System lower handguard. An advantage of using a 40mm grenade launcher on an assault rifle equipped with MIL-STD 1913 rails is the use of various range-finding optics.
The Canadian M203A1 by Diemaco (now Colt Canada) is a similar design with a different mounting system that does not require mounting points of the same profile as the M16A1 rifle's. The weapon's 9 inch barrel slides forward further than the standard American models to allow longer rounds to be loaded. This model is identifiable by the increased distance between the grenade launcher's barrel axis and the rifle's. This weapon may no longer be in production, but is still in use.
The M203A2 is intended for use with the M16A4 MWS (Modular Weapon System). Using standar 12 inch barrels, the grenade launcher is intended for use in concert with the Knight's Armament Company M5 RAS. Again, an advantage of this system is the usage of range-finding optics to make precise targeting easier.The M203PI system is used for attachment of the M203 to other rifles, including but not limited to the Steyr AUG, Heckler & Koch G3, and other rifles, and even the MP5 submachine gun. Most of these companies have since devised 40mm grenade launchers custom integrated with the weapon.
The M203 DAX has a double-action trigger and longer breech opening to accomodate less-lethal rounds.