The AR-15, which stands for "ArmaLite Rifle Model 15," is a modern sporting rifle that has its roots in the early 1960s. Designed by Eugene Stoner for ArmaLite, the AR-15 was later adapted by Colt Industries and adopted by the U.S. military as the M16 rifle. It operates on a direct impingement gas system, where gases from the fired round are channeled directly into the bolt carrier, which cycles the action to load the next round. This design allows for a lightweight, highly accurate, and modular firearm. The AR-15's popularity today stems from its adaptability and precision; it can be customized for various purposes, from target shooting to hunting to home defense. Its widespread appeal is also bolstered by the 5.56x45mm NATO cartridge it fires, which balances recoil and stopping power effectively. The AR-15's enduring legacy is a testament to its robust design, reliability, and the strong community of enthusiasts who appreciate its performance and modularity.