BBL SUB-ASSM 10.5IN MT 4140CM SBN 5.56Barrel Sub-Assembly 10.5" - 5.56x45mm - Barrel twist 1:7 - Barrel contour mt - Barrel material 4140cm, sbn - Barrel twist 1:7 - Muzzle thread 1/2-28 - Gas port location carbine - Finish sbnlocation carbine - Finish sbn: PS Guns and AmmoShop: PS Guns and Ammo