To fully take advantage of the performance of the 6mm ARC cartridge Brownells has teamed up with Faxon to offer these AR-15 6mm ARC barrels. Made from 416R stainless steel and finished with a black Nitride finish, these come in a heavy profile with a 1-8 5R twist rate, and 5/8-24 muzzle threads. Available in four different lengths here are the associated specifications: 14.5" length with Carbine length gas system and 0.069" gas port diameter 16" length with Mid-Length gas system and 0.079" gas port diameter 18" length with Mid-Length gas system and 0.079" gas port diameter 20" length with Rifle length gas system a Mfg: Faxon Firearms