An M4A1 with an M203 Attached

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The M203 is a single shot 40mm grenade launcher that can be attached to a variety of weapons. The M203 was created during the Vietnam War to replace the single-shot M79 grenade launcher, allowing grenadiers to be armed with a potent backup weapon (the M16 it is mounted on) rather than having to switch weapons. It is currently in use with the US military, though it is in the process of being replaced in US Army service with the Heckler & Koch M320 Grenade Launcher Module (GLM). The launcher comes in a number of barrel lengths, such as the original 12" model for the M16, the 9" model for the M4 carbine, and a 6" M203 PI system that can be mounted on many weapons, including the MP5. Unlike its Russian equivalent the GP-25 , the M203 is breech-loaded.


The M203 was the only part of the army's flechette rifle 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 conceptually similar Colt 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 system attached to an existing rifle. Because the size and weight of 40mm ammunition limits the quantities that can be carried on patrol, and 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 weapons.

It is sometimes argued that the M203 was a poor replacement for the M79, as while the M79 was quick to reload and more or less accurate under adverse conditions, such as in the Vietnam War, the M203 was more difficult and awkward to operate..

A new grenade launcher, the M320, will likely replace the M203 in United States service eventually. 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 was intended to be used as close fire support for point and group 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 non-armored vehicles. Its primary purpose is to engage enemies in dead space that cannot be reached by grazing fire. A well-trained M203 gunner can also use his 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 grenade. The M203 is not intended to be used against armored or heavy vehicles.


The M203 is able to fire a variety of different rounds for many purposes. There are 10 different rounds for the M203:

  • M406 High-Explosive round. Often called the 'H-E' round, this round is intended to produce kills and casualties on point and group targets, as well as destroying bunkers and doors. This round has a 5 meter 'kill zone' and a 15 meter 'casualty zone'.
  • M433 High-Explosive Dual Purpose round. Able to penetrate 2 inches of steel when fired straight at the target, it is designed to produce casualties and kills. This round has a 5 meter 'kill zone' and a 15 meter 'casualty zone'.
  • M585 White Star Cluster. Used for signaling and illumination.
  • M651 Tactical CS Grenade. Used for crowd and riot control, the round releases large amounts of CS gas to disable and scatter crowds.
  • M781 Practice round. Used for zeroing and qualifying on the M203. The tip is filled with orange chalk that creates a cloud on impact, allowing the spotter and scorer to see where the round hit, and can be used to zero the M203 sights.
  • Star Parachute. The White (M583A1), Green (M661), and Red (M662). Used to the same effect as the Star Cluster round for signaling and illumination purposes.
  • Ground Marker. The Red (M713), Green (M715), and Yellow (M716). Used as a signaling smoke grenade round to mark soldiers and targets.
  • M576 Buckshot ("Beehive") Contains 20 pellets of #4 buckshot. Used for room clearing and point blank firing. Essentially a 1.2-gauge shotgun shell.
  • M1006 Sponge Grenade. Used in crowd control situations where direct, non-lethal engagement of individuals is necessary. Manufacturer states that this round can be fatal within 10 meters.
  • M1029 Crowd Dispersal round. Somewhat like the M576 round except the projectiles are .48 caliber rubber balls weighing about 1.3g each. Manufacturer states that this round can be fatal within 10 meters and is ineffective outside of 30 meters.

Except for the Star Cluster, Star Parachute, Sponge Grenade, Crowd Dispersal round, and buckshot, all 40MM Grenade rounds are impact detonated. In addition the rounds have a minimum arming distance of 14 to 27 meters (though still capable of producing a causality with a direct hit at close range) and firers are advised to fire at targets more than 50 meters, the minimum safe stand off distance from an explosion.


The M203 Grenade launcher system comes with a variety of components, usually including the launcher, adaptors for attachment to assault rifles, and leaf sights (which can be used with the rifle's front sight post). M203s can also come with quadrant sights, mounting to a MIL-STD 1913 Rail, or to the carrying handle of an M16 rifle.


There are numerous variants of the M203 manufactured in the U.S., and throughout the world, for various applications. These vary chiefly in the length 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" 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", and principally the M203A1 QD is able to quickly detach from the rifle, and be replaced by a Knight's Armament Company M4 RAS lower handguard. An advantage of using a 40 mm grenade launcher on an assault rifle equipped with MIL-STD 1913 Rails is the attachment 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" 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.