The Heckler & Koch MR556A1 16" is a semi-automatic, piston-driven rifle that brings the combat-proven reliability of the military HK416 to the civilian market. VERY GOOD CONDITION ONE 30-RD MAGAZINE STRIKE INDUSTRIES KEYMOD HANDGUARD SYSTEM Key Specifications Caliber: 5.56x45mm NATO / .223 Remington Barrel: 16.5-inch cold hammer-forged, heavy-contour barrel Twist Rate: 1:7 inches Operation: Short-stroke gas piston (closed system) Capacity: 30+1 rounds Weight: Approx. 8.6 pounds Core Features Cleaner Operation: The closed gas piston system keeps exhaust gases out of the receiver, meaning the rifle runs cooler and cleaner than standard direct-impingement AR-15s. It accepts standard AR-15 grips, buffer tubes, and charging handles, though it uses a proprietary handguard and specific trigger group rules due to the firing pin safety.