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XM8 variants, from top: XM8 with XM320 40mm grenade launcher; XM8 Compact / PDW; XM8 Sharpshooter; XM8 Squad Automatic (drawing from H-K USA booklet)

Caliber: 5.56x45 mm NATO
Action: Gas operated, rotating bolt
Overall length: 838 mm in basic configuration, butt extended
Barrel length: 318 mm in basic configuration; also 229 mm in Compact and 508 mm in Sharpshooter and SAW versions
Weight: 2.659 kg empty in basic configuration
Rate of fire: ~ 750 rounds per minute
Magazine capacity: 30 rounds (STANAG) or 100-rounds double drum in Automatic Rifle/SAW role

The development of the XM8 Lightweight Assault Rifle was initiated by US Army in the 2002, when contract was issued to the Alliant Techsystems Co of USA to study possibilities of development of kinetic energy part of the XM29 OICW weapon into separate lightweight assault rifle, which could, in the case of success, replace the aging M16A2 rifles and M4A1 carbines in US military service. XM8 is being developed by the Heckler-Koch USA, a subsidiary of famous German Heckler-Koch company. According to the present plans, the XM8 should enter full production circa 2005, if not earlier, several years before the XM29 OICW. The XM8 (M8 after its official adoption) should become a standard next generation US forces assault rifle. It will fire all standard 5.56mm NATO ammunition, and, to further decrease the load on the future infantrymen, a new type of 5.56mm ammunition is now being developed. This new ammunition will have composite cases, with brass bases and polymer walls, which will reduce weight of the complete ammunition, while maintaining compatibility with all 5.56mm NATO weapons. Along with 20% weight reduction in the XM8 (compared to the current issue M4A1 carbine), this will be a welcome move for any infantryman, already overloaded by protective, communications and other battle equipment.

The XM8 will be almost similar to the "KE" (kinetic energy) part of the XM29 OICW system, being different mostly in having a telescoped plastic buttstock of adjustable length, and a detachable carrying handle with the sight rail.

As of November, 2003, first 30 prototypes of XM8 were delivered to US Army for initial testing, with further 100+ prototypes scheduled to enter tests early in 2004.

Technical description.
The XM8 is a derivative of the Heckler-Koch G36 assault rifle, and thus it is almost similar to that rifle in design and functioning. XM8 features a short piston stroke, gas operated action, with rotating bolt locking. Barrels are quick detachable, and planned to be available in several sizes, ranging from 229 mm (9.5 inch) for Compact/PDW version, 318mm (12.5 inch) in Basic version, and two 508mm (20in) barrels, one for Sharpshooter/Sniper version, and heavier one (along with bipod) for Squad Automatic Rifle role. The entire construction is modular and built around the polymer receiver with bolt group; Magazine housings could be easily swapped for compatibility with various types of magazines; various buttstocks could be installed in a second for various roles (standard buttstock is a telescoped 5 position adjustable one). Top of the receiver is fitted with proprietary sight rail, which can accept illuminated red-dot (collimator) sight, or any other type of sighting equipment. Detachable forend will be available in various sizes, and could be replaced with XM320 40mm grenade launcher (the improved HK AG36).

Ambidextrous fire controls are mounted on the trigger unit, integral with pistol grip and triggerguard, and in basic configuration are planned to deliver single shots and full auto fire. The G36-type ambidextrous charging handle is located at the top of the receiver, below the removable carrying handle.

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