CMMG's Mk4 T 300 Blackout Upper Group builds the foundation of a workhorse semi-automatic rifle. CMMG's RKM11 KeyMod™ free-float handguard adds attachment points for all types of tactical accessories for true modular customization. The medium-taper 16.1" barrel is crafted from 416 stainless steel with a bead-blasted finish, has 1:7 rate-of-twist rifling and comes equipped with an A2 muzzle threaded 5/8-24". Upper group components include forged 7075-T6 AL M4-type receiver; barrel sub assembly; charging handle; bolt-carrier group; handguard and barrel nut. Carbine gas port. Made in USA.