AR-15

The “AR” in AR-15 stands for ArmaLite Rifle — not for “assault rifle” or “automatic rifle” as commonly misconstrued. During the 1950s, ArmaLite developed the AR-15 as a military rifle. By 1959, the company sold the patent and manufacturing rights to Colt. Colt released the first civilian model — the AR-15 Sporter, a semi-automatic version chambered for .223 Remington — in 1964. Colt’s patents for the AR-15 expired in the 1970s, prompting other manufacturers to begin producing similar models based on its design. 

AR-15 style rifles have become so popular predominantly because of their versatility. They come in many sizes and with a multitude of options, depending on the manufacturer. The majority of AR-15s are chambered for the 5.56 NATO. However, they may be chambered in nearly any caliber — ranging from .22 long rifle to the massive .50 Beowulf.