CMMG was the first to bring a 4.6x30mm firearm to the U.S. civilian market continuing a tradition of innovation shooters everywhere can now build a light recoiling flat shooting PDW (personal defense weapon) like no other. Designed to work with any standard AR15 lower receiver and our 4.6x30mm magazines. Available in six different Cerakote finishes all CMMG Upper Groups come complete with bolt carrier group and ZEROED accessories including: – ZEROED AR15 Polymer Dust Cover – ZEROED AR15 Ambi Charging Handle – ZEROED Linear Compensator 5.56mm – Platform: Mk4 – Caliber: 4.6x30mm – Operating System: Direct Impingement – Barrel Length: 8 – Barrel Twist: 1:5.9 – Barrel Contour: MT – Barrel Material: 4140CM SBN – Muzzle Device: CMMG ZEROED Linear Compensator – Muzzle Thread: 1/2 x 28 – Gas Port Location: Micro – Gas Block: FourSix Specific .750 – Upper Receiver: Billet 6061 T6 Aluminum – Hand Guard: CMMG EML7 M-LOK – Finish: Cerakote Standard – Charging Handle: CMMG ZEROED Ambi – Weight: 3.2 lbs – Length: 16.5