ArmaLite AR-16

The AR-16 is a prototype selective fire, gas-operated rifle in 7.62×51mm NATO designed by Eugene Stoner at ArmaLite in the late 1950s. While the AR-16 never was adopted as a service rifle by any nation, its main claim to fame was that, in scaled-down form, it served as the basis for the more widely known 5.56mm AR-18, itself an influence on later designs. Despite the similarity in nomenclature, and while it is an ArmaLite design like the AR-15/M16, it is a very different weapon.

Eugene Stoner designed the AR-16 after the AR-15's direct gas impingement action was sold to Colt's Manufacturing Company. Stoner designed a more conventional weapon, using a more conventional short-stroke gas piston in place of the direct impingement system of the AR-15. The design was eventually used in the 5.56mm Armalite AR-18, but the AR-16 was only manufactured in prototype form and was never put into production. The AR-16 was Stoner's last design for ArmaLite; he left the company soon afterwards.

Construction and design
In place of the alloy forgings of the AR-10 and AR-15, the AR-16 was constructed from stamped steel upper and lower receivers and other components. Its action was powered by a short-stroke gas piston. The piston was of 3-piece design to facilitate disassembly, with a hollow forward section with 4 radial gas vent holes fitting around a stainless steel gas block projecting rearwards from the foresight housing. The gas was vented from the barrel and traveled via a vent through the foresight housing into the hollow front section of the piston, which caused it to move rearwards a short distance. The rear end of the piston emerged through the barrel extension to contact the forward face of the bolt carrier, causing it in turn to move rearwards. The bolt itself was of similar configuration to the AR-10 with 6 radial locking lugs engaging corresponding recesses in the barrel extension, with the extractor in place of the 7th lug and the 8th lug, opposite the extractor, ground short, so the support of the bolt is symmetrical. The bolt was moved into and out of the locked position via a cam pin that engaged a helical slot in the bolt carrier, which rode on two metal guide rods (each with its own return spring) instead of contacting the receiver walls, providing additional clearance for foreign matter entering the receiver. Unlike the AR-10, the cocking handle fitted directly into a recess in the bolt carrier and reciprocated with it during firing, allowing the firer to force the breech closed or open if necessary. The recoil springs were housed within the receiver, differing from the AR-10 which housed its more elaborate buffer mechanism in the buttstock. The AR-16's compact design enabled the use of a side-folding stock with a hinging mechanism.

The sights were of similar design and sight picture to those of the AR-10 - a 2-position flip aperture rear sight and post foresight - but the rear sight was made of stampings. A notable change is the use of a more conventional lower sight line closer to the axis of the bore, in contrast to the elevated sights of the AR-10.

Overall, the design is simple and effective with some clever touches; for example the bolt guide rod assembly guides the bolt in the receiver, retains the recoil springs and the rear end of the top handguard, as well as serving as the latch holding the upper and lower receivers together in the closed position. Disassembly is somewhat similar to the AR-10 and AR-15, with the working parts accessed by the rifle pivoting open on a cross-pin immediately forward of the magazine well.

AR-16 derivatives
Despite its lack of commercial success, the AR-16's basic design features have been reused in several other firearms. These include:


 * Armalite AR-18, Main derivative of the AR-16
 * L64/65/SA80
 * SAR-80/SR-88/SAR-21
 * Sterling SAR 87
 * Leader Dynamics Series T2 MK5
 * Howa Type 89
 * Bushmaster M17S
 * Heckler & Koch G36
 * Heckler & Koch HK416
 * T65 assault rifle