Patented chrome-plated, two-stage piston with multi-stage regulator provides a cleaner, cooler running, reliable firearm with superior operating endurance. The two-stage piston provides a smooth power delivery stroke to the bolt carrier. Lower receiver is fitted with the Magpul® MOE® grip and MOE SL™ collapsible buttstock on the mil-spec buffer tube. Precision-rifled, chrome-lined, cold hammer-forged Mil-Spec 41V45 chrome-moly-vanadium steel barrel ensures accuracy and longevity. A Ruger® flash suppressor is provided, and the 1/2″-28 threaded barrel allows for standard muzzle accessories to be installed. Slim, lightweight KeyMod™ handguard for reduced overall weight.