The AR-15 was originally made for a 5.56 NATO cartridge developed for the US Armed forces as a lighter more mobile rifle than the M14 in 7.62x51 NATO. It was first designed by Eugene Stoner, an American mechanical engineer. The AR-15 is a lightweight direct impingement rifle making it a low recoil rifle that is easy to shoot accurately over long distances. The select fire version was adopted by the military as the M-16. The original manufacturer of the AR-15 was ArmaLite, Inc., with “AR” standing for ArmaLite Rifle.  In 1959 Colt purchased the “AR-15” trademark from ArmaLite and in January of 1964 started selling the semi-auto version the Colt AR-15 SP-1 to the public. Many are misled to believe that the AR stands for Assault rifle which is not the case. Colt termed the civilian version right at the beginning with “SP-1” as in Sporter Rifle 1.” They later offered different models like the Colt Sporter Match Target” and Sporter Lightweight and Sporter Competition model just to name a few. In 1988 the intellectual property rights expired, allowing other manufacturers to make AR15-style rifles (clones). A better term for AR15-style rifles would be MSR, as in Modern Sporting Rifle. Even though they are essentially the same rifle, the only true AR-15s are made by Colt with the AR-15 roll mark. Every brand has its model name for its AR15-style rifle based on the Stoner Design. This opened the door for the development of commercial parts and accessories and different cartridges such as 6.5 Grendel, 6.5SPC, 300 Blackout, 458 SOCOM, and more. It is the most popular rifle in America. It is widely used for competition, law enforcement, hunting, and defense.