Thanks to the foresight of Gene Stoner and his team of designers and engineers, the Armalite Rifle model 15 was first conceived in the late 1950’s. Stoner’s design varied from traditional military service rifles by replacing hardwood stocks and forearms with those made from polymer. Also, the weight of the rifle was reduced by using aircraft grade aluminum in many places instead of steel.
When the United States Air Force became interested in the new light-weight, aluminum and polymer rifle, Colt Firearms came up with a number of designs. The XM16E1 bridges the gap between the Model 601 and what would be adopted as the standard service rifle; the M16A1.
The “X” in XM stands for experimental. This is a product not yet officially adopted by the US Army, but under direct evaluation by putting it in the field. There were a few changes added to the XM16E1 from the Model 601. For instance, a forward assist was added to the right side of the upper receiver. The 3 prong flash-hider was modified from the “duckbill” style and the 20 round “waffle” magazine of the M601 was altered to the more familiar current design. Also, the stock and forend of the M601 were green, the XM16E1 used the now standard black.
As for specifics; the XM16E1 uses a 20 inch barrel with a 1 in 12 twist rifling. The bolt and bolt carrier are chrome. The rifle chambers the 5.56x45mm NATO rifle cartridge and the standard magazine holds 20 rounds, 30 round magazines would be introduced around 1970 after the official adoption of the M161A1 but the US Army.
The original XM16E1 used a 3 position selector lever with “safe”, “semi”, and “auto” choices. Overall length is 40 inches and the empty weight is 6 pounds, 11 ounces. Forward and rear sling swivels are included. The sights are fully adjustable; windage is adjusted in the rear and elevation is adjusted with the front sight. Sight adjustments can be made by using the tip of a 5.56mm rifle cartridge. No tools are required to field strip the rifle for cleaning. The aluminum parts are anodized gray and the steel parts are parkerized.
A bayonet lug is included as a part of the “A frame” front sight housing. The M7 bayonet was specifically developed for use with the M16 series of rifles and carried in an M8a1 sheath.