The trademark "AR15" or "AR-15" is registered to Colt Industries, which maintains that the term should only be used to refer to their products. Other manufacturers make AR-15 clones marketed under separate designations, although colloquially, these are sometimes also referred to by the terms
"AR-15" and "AR-15 Platform".
The AR-15 (ArmaLite Model 15) is a widely owned semi-automatic rifle, of which the most famous derivative is the selective fire (Full-Auto / Semi Auto) M16 series assault rifle used by the United States military. The "AR" in AR-15 comes from the ArmaLite name.
Standard AR-15 rifles accept detachable magazines of widely varying capacities, most common are 10, 20, or 30 round magazines, but other capacities are also available, in addition to various drum magazines, and have a pistol grip that protrudes beneath the stock.
The AR-15 is a lightweight, air-cooled, magazine-fed, autoloading, centerfire rifle that fires a .223 Remington Cartridge. The original Armalite/Colt AR-15 was a selective-fire prototype submitted for consideration as a military infantry rifle, and is distinguished from later civilian-model AR-15 and AR-15A2 rifles marketed by Colt Firearms.
The AR-15 is based on the 7.62mm AR-10, designed by Eugene Stoner of the Fairchild ArmaLite corporation. The AR-15 was developed as a lighter, 5.56mm version of the AR-10.
ArmaLite sold its rights to the AR-10 and AR-15 to Colt in 1959. Colt marketed the AR-15 rifle to various military services around the world, including the U.S. Air Force, Army, and Marine Corps. The AR-15 was eventually adopted by the United States military under the designation M16.
However, Colt continued to use the AR-15 trademark for its semi-automatic variants (AR-15, AR-15A2) marketed to civilian and law-enforcement customers. The original AR-15 was a very lightweight weapon, weighing less than 6 pounds with empty magazine.
Today the civilian-model AR-15 and its variations are manufactured by many companies and have captured the affection of sport shooters and police forces around the world due to their low cost, accuracy, and modularity.
Semi-automatic variants of the AR-15 are effectively identical in appearance. In semi-automatic only variants, the selector only rotates between safe and semi-automatic.
The AR-15 rifle is available in a wide range of configurations from a number of manufacturers. These configurations range from short carbine-length models with features such as adjustable length stocks and optical sights, to heavy barrel models.
Aftermarket AR-15 upper receivers that incorporate barrels of different weights and lengths, and handle different caliber ammunition, abound for this rifle. They are very easily installed, due to the rifle's modular design.