Real Rifle History;
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[1] and was introduced to U.S. military forces during the early 1970s, replacing the M79 grenade launcher and the 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 device attached to an existing rifle. Because the size and weight of 40 mm 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 the two.
 
Features:
It comes with several mounting options so can be fitted to most M4/M16 platforms.