The Ruger AR-556 MPR Semi-Auto Rifle operates with direct-impingement and a rifle-length gas system. The lower receiver comes equipped with a Magpul MOE pistol grip and a MOE SL 6-position, collapsible buttstock on a Mil-Spec buffer tube. Upper and lower receivers are CNC-machined from 7075-T6 aluminum forgings and Type III hard-coat anodized for maximum durability. A 15” free-float, M-LOK handguard features accessory attachment slots at 3:00, 6:00 and 9:00 positions, and a continuous Picatinny rail interface with the flat-top, railed, upper receiver. The upper receiver features a forward assist, dust cover, and brass deflector. A Ruger Elite 452 2-stage, AR-Trigger offers a smooth, crisp break at approximately 4.5 lbs. The bolt carrier and gas key have chrome-plated inside diameters to provide exceptional resistance to hot gases; and the gas key is securely staked to prevent loosening during extensive fire. The cold hammer-forged 4140 chrome-moly steel barrel comes with an M4 feed ramp, and black Nitride finish; a 1:8” rifling twist rate maximizes accuracy with bullets ranging from 35 to 77 grains. A Ruger radial-port flash suppressor is attached to the barrel with a 1/2”:28 thread.