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XM8 Lightweight Assault Rifle

Type: Assault rifle
Place of origin: Germany, United States
Production history
Designed: 2002
Manufacturer: Heckler & Koch
Produced: 2003–2004 (prototypes only)
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Cartridge: 5.56x45mm NATO
Action: Gas-operated, rotating bolt
Rate of fire: 750 rounds/min
Muzzle velocity: 920 m/s
Feed system: 30-round detachable box magazine, 100-round C-Mag drum magazine
Sights: Unmagnified reflex sight (4x for DMR variant)

The US Army's purpose in contracting for this prototype weapon was to provide replacement options for the venerable M16 rifle 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.

The XM8 was based on the kinetic energy module of Alliant Techsystems's XM29 OICW project, of which the weapon mechanisms were the responsibility of H&K. Following the indefinite delay of the Objective Individual Combat Weapon program, the U.S. Army requested that the contractors design stand-alone weapons from the XM29's kinetic energy and high explosive modules.

The first 30 XM8 prototypes were delivered by November 2003 for preliminary testing. Later, at least 200 developmental prototypes were procured. Among the complaints during testing were too low a battery life for the weapon's powered sight system and some ergonomics issues. Two other key issues were reducing the weapon's weight and increasing the heat resistance of the hand guard, which would start to melt after firing too many rounds. The main testing was largely completed, and the Army pushed for funding for a large field test. However, in 2004 Congress denied $26 million funding for 7,000 rifles to do a wide scale test fielding of the XM8 in 2005. At the time the rifle still had developmental goals that were incomplete, primarily associated with the weapon's weight; the battery life had been extended, and a more heat-resistant plastic hand-guard added. The earliest product brochure lists the target weight for the carbine variant at 5.7 lb (2.6 kg) with the then current prototype at 6.2 lb (2.8 kg). The weight of the carbine prototype had since grown to 7.5 lb (3.4 kg) according to a brochure released by HK and General Dynamics in January 2005.

During the same period, the Army came under pressure from other arms makers to open up the XM8 to competition. The main argument was that the weapon that was being adopted was a substantially different system than for the original competition that ATK and H&K had actually won (see XM29). Other issues were that the Army has a legislated obligation to prefer U.S.-based manufacturers, and that a previous agreement with Colt Defense required the Army to involve Colt in certain small-arms programs. The XM8 program was put on hold by the Army in 2004. The exact reason why this happened is a matter of debate; some combination of the aforementioned technical issues, funding restrictions, and outside pressure being involved.
In 2005, the Army issued a formal Request for Proposals (RFP) for the OICW Increment One family of weapons. This RFP gave manufacturers six months to develop and deliver prototype weapons with requirements very similar to the XM8 capabilities, but with the addition of a squad automatic weapon (SAW) configuration. Currently, no XM8 prototypes have been shown that actually match the capabilities of the M249 (e.g. fast barrel replacement, high sustained rate of fire, belt feed). The OICW Increment One requirement for the SAW includes fast barrel replacement and high sustained rate of fire, but leaves the ammunition feed choice up to the manufacturer.

Funding for the XM320 grenade launcher, which is a single-shot under-barrel grenade launcher similar to the M203 that was originally intended for the XM8, was approved. The launcher is actually heavier than the M203, but does offer some advantages. The XM320 was designed for use with the existing inventory of M16s and M4s and is also compatible with the XM8. It can also be used as a stand-alone weapon.

As of July 19, 2005, the OICW Increment One RFP was put on an eight-week hold, with an indication given that the program was being restructured as a joint procurement program including the Army and unnamed other branches. On October 31, 2005, the OICW Increment One RFP was canceled until further notice.

In an article in Jane's Defence Weekly, April 26 2006 (Vol 43, page 30) we learn that "The US Army has again delayed the procurement of its future infantry weapons, this time for more than five years, and is working to field two interim guns in the meantime."

Technical characteristics and variants

For much of its life, four different models were proposed: a compact PDW (personal defense weapon) with a 9.5 inch (241 mm) barrel, a carbine with a 12.5 inch (318 mm) barrel, and sniper and automatic rifle variants with 20 inch (508 mm) 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 mm 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.
One of the XM8's unique features was its modularity. In addition to attachments mentioned above, this modularity allowed for quick repairs, barrel length changes, and even caliber changes in the field. Along with its basic components, the XM8 would have complemented the XM29, with such features as identical accessory mounts.

The number and type of variants in the family varied over its lifetime, this overview with three main versions is based from a press release in the early 2000s.

XM8 Carbine with XM320 grenade launcher

XM8 Compact Carbine: 9 in (229 mm) barrel, PDW configuration, folding stock or buttcap.

Automatic Rifle / Designated Marksmen: heavy 20 in (508 mm) barrel, integrated folding bipod, 4X sight, 30/100 round magazine
Materials and Weight
The materials used to build the XM8 are almost entirely composites — with the notable exception of the cold hammer forged steel barrel. Preliminary tests in desert and Arctic conditions have shown XM8 to be a rugged weapon, though some complaints arose. It is reported to be capable of firing 15,000 rounds without cleaning or lubrication and up to 20,000 rounds before barrel replacement. The M16A2 needs to be cleaned often, and has a barrel life of approximately 7,000–8,000 rounds.

Much of the cost and weight savings, not all of which have actually been achieved in the current prototypes, are from the weapon's electronic sight. The sight is much more than a 1.5x red dot scope, including IR lasers and pointers as well. The baseline XM8 carbine (with its integrated sight), for example, can be compared to an M4 carbine with a host of previous-generation electronic add-ons like the AN/PEQ-2, M68 CCO, ACOG, and/or BUIS. Without the advantage of the next-generation combined electronics sight, the XM8 would be both heavier and more expensive than the firearms it is intended to replace. The XM320 grenade launcher intended to be used with the current M4/M16 firearms as well as the XM8 family, is heavier than the M203, but does include feature enhancements.
PCAP and MIL-STD-1913
XM8 abandons the standard MIL-STD-1913, for attachment of weapon accessories, in favor of a new standard referred to as PCAP (Picatinny Combat Attachment Points), small oval holes on the forward grip. (A variant was designed with MIL-STD-1913 rails — XM8 R — and some early XM8 prototypes had rails.) PCAP is not backwards compatible with currently fielded attachments that use MIL-STD-1913 rails without using an adapter. The benefit of PCAP, however, is the precision of the accessory's connection with the body of the weapon; accessories utilizing MIL-STD-1913 rails often need adjustment if they are removed and reattached. Additionally, most standard accessory functionality is built-in to the XM8. Where functionality was missing, it was anticipated that accessories would be redesigned to utilize PCAP. In the new OICW Increment One competition, the Army has left the choice of attachment technology up to the manufacturer, with requirements built into the RFP as to the ability of sights to maintain their zero.

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