Made with pride in the USA, CMMG's Upper MK4 B18 5.56mm Upppers builds the foundation of a workhorse semi-automatic rifle. CMMG's RKM14 KeyMod™ free-float handguard adds attachment points for all types of tactical accessories for true modular customization. The 18" barrel is crafted from 416 stainless steel with a heavy bull profile for improved shot consistency, has 1:7 rate-of-twist rifling and comes equipped with a target-crown muzzle. Forged 7075-T6 AL M4-type receiver. Made in USA.