There is a reason why the AR-15 is the best selling rifle in the United States. For its versatility, flexibility, modular design, and ease of use, everyone from beginners to expert shooters love the AR-15—the modern sporting rifle. The love for the AR-15 derives from how easily it is to customize and change. It goes from self-defense to competition to hunting to plinking with a few minor adjustments and accessories. Accessories and add-ons are widely available. Created by ArmaLite Chief Engineer Eugene Stoner the semi-automatic AR-15 uses either a direct gas impingement or gas piston system to operate. Originally chambered for the .223 Remington/5.56 NATO round, now you can find AR platforms in a variety of calibers such as .22 Long Rifle, .300 Blackout, 6.8 SPC, and .450 Bushmaster.