*information from distribution website: CMMG, Barrel, 300 AAC Blackout, 16.1" Barrel, 1:7 Twist, Carbine 416 SS Bead Blasted Finish, 5/8"-24 TPI, 1:7 Twist 416 Stainless steel, 5/8X24 thread pitch, Medium taper profile, Carbine length gas port .750" gas block Journal, 300 Blackout chamber Description: Perfect for building your custom AR15 upper group. Comes with properly installed M4 barrel extension. All barrel sub-assemblies are properly head spaced. *Buyer must provide photo identification & address verification upon purchase via email - instructions will be provided once purchase is confirmed - Signature required.