(Also known as modern sporting rifle, MSR, M4, M16, M400, black rifle.) The most popular rifle in America, the AR-15 shares the some of the design with the military M-16 and M-4 rifle, but operates as a semi-automatic only firearm legal for civilian use. Designed by Armalite’s Eugene Stoner, the AR-15 (which is short for Armalite Rifle Model 15) was first chambered in 223 caliber and was the follow-up design to the AR-10 in the U.S. Military’s search for a replacement to the M1 Garand. In the late 1950s, Armalite sold the design to Colt Manufacturing Company who then manufactured both a civilian version—that fired in semi-automatic mode—and a military version that fired in both semi-automatic and full-auto. The U.S. Military adopted a “select fire” version of the AR-15, designating it the M-16 and first fielding it to troops fighting in Vietnam. Since then, “AR-15” has become a term used to describe rifles derived from the original Armalite- and Colt-made rifles, featuring a magazine-fed, gas-operated, rotating bolt design with a pistol grip. The firearms industry group The National Shooting Sports Foundation adopted the term “Modern Sporting Rifles” to describe firearms using this design and manufacturers have developed a wide variety of models using the same fundamental operating system and ergonomics as Eugene Stoner’s original rifle.