The CMMG Mk4 is a semi-automatic AR-15 rifle chambered for 5.56x45mm. It features forged 7075-T6 aluminum M4 type upper and AR-15 type lower receivers nitrided 4140 chromium-molybdenum alloy steel M4 profile 16.1 threaded barrel RKM11 KeyMod free-float handguard single stage mil-spec style trigger and standard A2 compensator. This rifle sports an A2 pistol grip and M4 buttstock with six position mil-spec receiver extension as well as a mid-length gas port location. Details The Mk4 RCE is one of CMMGs premiere rifles. The Mk4 RCE features a 16 416 stainless steel medium taper profile barrel available in either 5.56x45mm or 300 BLK. The RCE is equipped with CMMGs own SV muzzle brake and RKM14 KeyMod hand guard. Every rifle has a Geissele SSA 2-stage trigger and Magpuls MOE pistol grip MOE trigger guard and CTR butt stock installed. - Caliber 223 Rem 5.56mm NATO - Action Semi-Automatic - Finish Stainless - Material Steel - Twist 1.7 - Barrel 16.1 - Sights None - Weight 6.7 lbs - Overall Length 34 - Muzzle CMMG SV brake threaded 12-28 - Hand Guard CMMG RKM14 KeyMod hand guard - Receivers Forged 7075-T6 AL M4 type upper AR15 type lower - Trigger Geissele Automatics SSA - Gas Port Location Mid-length