UPPER GROUP RESOLUTE Mk4 5.56X45MM NATO 16.1 - Top off your next build with this RESOLUTE� Mk4 Upper Group. Chambered in 5.56x45mm this upper group is a staple for any collection and comes ready to pair with the AR15 lower group of your choice. Available in different Cerakote finishes all CMMG� Upper Groups come complete with bolt carrier group and ZEROED ambi charging handle. - Specifications - Platform Mk4 - Caliber 5.56x45mm - Operating System Direct Impingement - Barrel Length 16.1 - Barrel Twist 1:7 - Barrel Contour MT - Barrel Material 4140CM SBN - Muzzle Device CMMG ZEROED Muzzle Brake - Muzzle Thread 1/2 x 28 - Gas Port Location Mid - Gas Block Adjustable 0.750 - Upper Receiver Billet 6061 T6 Aluminum - Hand Guard CMMG EML15 M-LOK - Finish Cerakote Standard - Charging Handle CMMG ZEROED Ambi - Weight 4.3 lbs - Length 25