M203 40mm Grenade Launcher

Gary's U.S. Infantry Weapons Reference Guide

The M203-series grenade launchers are lightweight, single-shot, breech-loaded, pump action (sliding barrel), shoulder-fired weapons. The grenade launcher is composed of the following: barrel, receiver, hand guard, leaf sight, and quadrant sight.
Replaced the M79 grenade launcher in U.S. service. Will be replaced by the M320 grenade launcher.

M203 (NSN 1010-00-179-6447)

1969. Original production model. Designed for use with M16-series rifles.

M16A1 with M203
23-OCT-1991
U.S. DoD Photo
2048x700, 957K, PNG

Practice round loaded into M203 on M16A1
26-AUG-1988
U.S. DoD Photo
2048x1373, 792K, JPEG

M16A2 with M203
U.S. Air Force Photo
2100x586, 331K, JPEG

M203A1 (NSN 1010-01-434-9028)

Designed for use with M4-series carbines. It is functionally identical to the M203.

M203A2 (NSN 1010-01-495-8511)

Has a quick-release bracket for use with M4 and M4A1 carbines that have the M4 rail system and with M16A4 rifles that have the M5 adapter rail system.

U.S. Air Force Photo
2100x824, 322K, JPEG

The grenadier's operations include loading, unloading, and firing the weapon.

The weapon uses a high-low propulsion system to fire a 40mm round. The firing pin strikes the primer, whose flash ignites the propellant in the brass powder-charge cup inside the high-pressure chamber. The burning propellant produces 12,000 psi chamber pressure, which ruptures the brass powder-charge cup at the vent holes and allows the gases to escape to the low-pressure chamber in the cartridge case. There the pressure drops to 3,000 psi and propels the grenade from the muzzle at a velocity of 250 fps. The grenade's 3,700-rpm right-hand spin stabilizes it during flight and applies enough rotational force to arm the fuze.

The weapon is unloaded with the barrel open and fired from a closed bolt. It must be cocked before it can be placed on safe.

Cycle of functioning:

1. Unlocking. The cycle begins when the grenadier depresses the barrel latch to unlock the barrel assembly and slides the barrel assembly forward.
   
   
   
2. Cocking. The grenadier moves the barrel assembly forward, then backward, to cock the weapon. As the barrel assembly moves, it takes with it the barrel extension. Their movement causes the following to occur:
   • The cocking lever is forced down as the barrel assembly and barrel extension, which are interlocked with the cocking lever, move forward.
   • The movement of the cocking lever forces the spring-loaded firing pin to the rear.
   • The spring-loaded follower also moves forward with the barrel extension.
   • The barrel assembly continues forward, disengaging the barrel extension from the cocking lever. The cocking lever is then held down by the follower.
   • When the grenadier begins to move the barrel assembly back to the rear, this forces the follower to the rear.
   • The cocking lever again engages the barrel extension, which causes the firing pin to move slightly forward and engage the primary trigger sear. This cocks the weapon.
   
   
   
   
3. Extracting. Extracting and cocking occur at the same time. As the grenadier opens the barrel assembly, a spring-loaded extractor keeps the live round or spent cartridge case seated against the receiver until the barrel clears the cartridge case.
   
   
   
4. Ejecting. The spring-loaded ejector pushes the live round or spent cartridge case from the barrel assembly. As the grenadier opens the barrel assembly, a spring-loaded extractor keeps the live round or spent cartridge case seated against the receiver until the barrel clears the cartridge case.
   
   
   
5. Loading. With the barrel assembly open, the grenadier inserts a round into the breech end of the barrel.
   
   
   
6. Chambering. As the grenadier closes the breech end of the barrel assembly, the extractor contacts the rim of the cartridge and seats (chambers) the round firmly.
   
   
   
7. Locking. As the barrel assembly closes, the barrel latch engages it. The cocking lever engages the barrel extension so that it cannot move forward along the receiver assembly.
   
   
8. Firing. When the grenadier pulls the trigger, the primary trigger sear disengages from the bottom sear surface of the firing pin. This releases the spring-driven firing pin, forcing it forward against the cartridge primer
   
   
   

Ammunition for the M203 is issued in the form of a complete, fixed round. Click here for more information.

For short range targets (31 meters (102 ft) or less), place leaf sight down and use rifle sights. Estimate distance to target and be sure to aim at the foot of the target (M576 round).

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For targets from 50 to 250 meters (165 to 820 ft), raise leaf sight and use with rifle front sight. For targets from 50 to 400 meters (165 to 1320 ft), use front and rear sight of the quadrant sight only.

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The launcher may be fired from standing, kneeling, or prone position. When firing long range from prone position, place stock of weapon on the ground. For all other positions, hold stock firmly against shoulder.

When firing high explosive (HE) grenades at targets within 165 meters (541 ft) (minimum safe), be in a protected position. When training (minimum safe), do not fire at targets within 165 meters (541 ft). When in combat, do not fire at targets closer than 31 meters (102 ft).


The M203 has the inherent accuracy to place grenades into windows at 125 meters (410 ft) and bunker apertures at 50 meters (164 ft). These ranges are significantly reduced as the angle of obliquity increases. Combat experience shows that M203 gunners cannot consistently hit windows at 50 meters when forced to aim and fire quickly.