For those builders who already have barrel parts, we offer this M4 Profile Crowned Barrel Sub-Assembly with MIL-STD-1913 Railed Gas Block. The highly accurate 4150 Chrome Moly Vanadium steel barrel is chrome lined and rifled 1 x 9″ Right Hand twist. The muzzle is finished with a plain crown to comply with legal restrictions in States where threaded muzzles and flash hiders are prohibited – the bayonet lug has been machined off the MIL- STD-1913 Railed Gas Block. The Assembly includes Barrel, Barrel Extension with M4 Feed Ramps, Barrel Nut, Front Handguard Cap, MIL-STD-1913 Railed Gas Block with Sling Swivel. All top quality Windham Weaponry parts – made in the USA.