The XM8 was a developmental U.S. military designation and project name for a lightweight, assault rifle system that was under development by the United States Army from the late 1990s to early 2000s. The Army worked with the German small arms manufacturer Heckler & Koch (H&K) to develop the system to its requirements in the aftermath of the OICW contract, for which H&K had been a subcontractor to ATK. Although there were high hopes that the XM8 would become the Army's new standard infantry rifle, the project was put on hold in April 2005, and was formally cancelled on October 31, 2005.
The U.S. Army's purpose in contracting for this prototype weapon was to provide replacement options for the venerableM16 after the XM29 program ran into problems. The Army's goal was a weapon that was cheaper, lighter, and more effective than the M16 and M4 Carbine series of weapons. The XM8 was not just one weapon, but a system which could be reconfigured with appropriate parts to be any one of several variants from a short-barreled personal defense weapon to a bipod-equipped support weapon. It also included an integrated optical sight and IR laser aiming module/illuminator.
For much of its life, four different models were proposed: a compact PDW (personal defense weapon) with a 9.5-inch (241mm) barrel, a carbine with a 12.5-inch (318mm) barrel, and sniper and automatic rifle variants with 20-inch (508mm) barrels. In addition, accessories such as optical sights, a grenade launcher, and a bipod were integrated using a new system which allows for precision attachment (so that, for example, scopes do not have to be readjusted each time they are attached). Like the M4 and M16, the XM8 was chambered for the standard 5.56 NATO round and was normally equipped with a 30-round plastic box magazine. However, this magazine was not compatible with M4 and M16's metal STANAG magazine. A 100-round dual drum Beta C-mag style magazine would have been used, as well.