Douglas 18" Black Cerakoted 416 stainless steel barrel with 1-7 twist and M4 feed ramps. Barrel is medium SPR profiled barrel, threaded with a 1/2-28 thread for the AE brakes and collar. this is the barrel designed and profiled for the Mark 12 Mod 0 uppers and rifles. Gas block area is .750 diameter. Barrel uses a rifle length gas system and is chambered in 5.56 Nato