With an impressive 40-round magazine capacity light recoil and great penetration at close distances the CMMG® FourSix is here to reimagine the Personal Defense Weapon. Not only is the FourSix the first AR chambered in 4.6x30mm but it is also the first 4.6x30mm firearm ever released to the U.S. civilian market! – Platform Mk4 – Caliber 4.6x30mm – Operating System Direct Impingement – Barrel Length 8 – Barrel Twist 1:5.9 – Barrel Contour MT – Barrel Material 4140CM SBN – Barrel Twist 1:5.9 – Muzzle Device CMMG ZEROED Linear Comp – Muzzle Thread 1/2 X 28 – Gas Port Location Micro – Gas Block FOURSIXTM Specific .750 – Upper Receiver Billet 6061 T6 Aluminum – Lower Receiver Mk4 Forged 7075 T6 Aluminum – Hand Guard CMMG EML7 M-LOK – Finish Cerakote Standard – Charging Handle CMMG ZEROED Ambi – Pistol Grip CMMG ZEROED Pistol Grip – Buffer Type Carbine – Receiver Extension CMMG 6 Position Fastback Extension – Stock / Brace CMMG RipBrace – Trigger Type ZEROED Drop-In Single Stage – Trigger Guard CMMG ZEROED Trigger Guard – Safety Selector CMMG ZEROED 60/90 Degree – Magazine CMMG 40rd – Weight 4.3 lbs – Length 23.7