Armalite AR - 16 The AR - 16 is a prototype selective fire , gas - operated rifle in 7 . 62x51mm 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 7 radial locking lugs engaging corresponding recesses in the barrel extension , and the extractor in place of the 8th lug . 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 cocking handle slot had a spring - loaded cover that could be closed by the user to prevent debris entering the receiver , and it would open automatically as the bolt carrier moved rearwards after the first shot . 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 :