In comparison to the ubiquitous direct-impingement system seen on most of today's AR-15s, gas-piston systems offer some benefits that make the alternate setup attractive to many AR aficionados. Gas-piston systems introduce less fouling into the gun's receiver, and the setup of the long-stroke piston system found on the Primary Weapons MK-116 Pro Rifle allows users to fine-tune gas flow for specialized uses. Each MK-116 Pro Rifle is chambered in .223 Wylde, allowing users to run either .223 Rem. and 5.56 NATO with increased accuracy. The long-stroke system on the gun, while remaining affordable compared to other piston-driven guns, also provides three different settings for us Mfg: Primary Weapons