The AR-16 is a prototype select-fire, gas operated assault rifle made by ArmaLite after the US Military adopted and bought the designs of the AR-15 and M16. The AR-16 was only manufactured in prototype form and was never put into production. The AR-16 was Eugene Stoner's last design for ArmaLite; he left the company soon afterwards.
Eugene Stoner had been trying to start a new design on the operation of weapons after the AR-15's expanding gas action was bought by the US Military and Colt. He tried using the short stroke gas-piston. It never was finished, though, as after ArmaLite was reorganized, Stoner left. The design was eventually used in the 5.56x45mm NATO Armalite AR-18, but the AR-16 never became an issued rifle.