It uses the same rounds as the older stand-alone M79 break-action grenade launcher, which utilizes the high-low propulsion system to keep recoil forces low.

While compatible with many weapons, the M203 was originally designed and produced by the United States military for the M16 rifle and its carbine variant, the M4.

The M203 has been in service since 1969[1] and was introduced to US military forces during the early 1970s, replacing the M79 grenade launcher and the conceptually similar Colt XM148 design.

[6] 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 round is designed to be effective at breaking through windows and exploding inside, blowing up doors, producing multiple casualties, destroying bunkers or emplacements, and damaging or disabling soft-skinned vehicles.

While classified primarily as an anti-personnel weapon, the shaped charge featured in the HEDP round gives it the capability to penetrate lightly armored vehicles.

[17] The weapon's 9 in (23 cm) barrel slides further forward than the standard American models, which allows longer rounds to be loaded.

Using standard 12 in (30 cm) barrels, the grenade launcher is intended for use in concert with the Knight's Armament Company M5 RAS.

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 the MP5 sub-machine gun.

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.

[19] In the United States, M203 grenade launcher attachments fitted with the standard rifled 40 mm barrels are classified as "destructive devices" under the National Firearms Act (NFA) part 26 U.S.C.

New M203 launchers sell for approximately $2,000 plus a $200 transfer tax, and new manufacture 40 mm training ammunition is available for $5 to $10 per cartridge, as of March 2011.

There are also sub-caliber adapters available for the 40 mm M203 (and M79) grenade launchers, which will allow the use of standard 12-gauge shotgun shells[45] and .22 rimfire ammo.

As the 37 mm version is not classified as a "destructive device", it can be sold to the general public on the same ATF Form 4473 as most other firearms.