M203 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, and requires the bottom handguard on the rifle to be removed in order to mount the launcher. 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. 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.

History
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.

Uses
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. A well trained 203 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 was not, and is not intended to be used against armored or heavy vehicles.

Rounds
The M203 is able to fire a variety of different rounds for many purposes. There are 8 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 at night time.
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.
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.

Buckshot - Used for room clearing and point blank firing. Much like a very large shotgun shell.
Except for the Star Cluster and Star Parachute, all 40MM Grenade rounds are impact detonated. In addition the rounds have a minimum arming distance of 14 to 27 meters, and firers are advised to fire at targets more than 50 meters, the minimum safe stand off distance from an explosion.

Components
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.

Variants
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.

The M203A2 is intended for use with the M16A4 MWS (Modular weapon system). Using standard 12" 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 attachment of range-finding optics makes precision targeting easier.

The M203 PI system is used for attachment of the M203 to other rifles, including but not limited to the Steyr AUG, H&K G3 and other rifles, and even the MP5 submachine gun. Most of these other companies have since devised 40 mm grenade launchers custom integrated with the weapon.

The M203 and M203A1 are currently manufactured by Airtronic USA, Inc. of Elk Grove Village, Illinois for the U.S. Department of Defense under contract numbers W52H09-06-D-0200 and W52H09-06-D-0225. Each contract is for up to 12,000 units. Each unit is shipped with hand guard, leaf sight and quadrant range sight. The contracts unit prices vary from $840 to $1,050 each. The production rate is 1,500 units per month. The M203 PI is manufactured for both U.S. Department of Defense and for commercial sales (to Law Enforcement agencies both in the USA and abroad, and for foreign military sales) by RM-Equipment Inc. of Miami, Florida.