CMMG Inc Barrel Sub-Assembly Light Taper 5.56mm 16.1in 4140CM Salt Bath Nitride. Comes with properly installed M4 barrel extension. All barrel sub-assemblies are properly headspaced. Features of CMMG Inc 5.56x45mm Nato Mk4 Barrel Sub Assembly - 12.5inch Mr 4140cm Sbn 5.56mm: 12.5" Multi Role Profile 4140 Chrome Moly Salt Bath Nitride Finish inside and out 1:7 Twist 5.56 45 NATO Chamber Threaded 1/2-28 Carbine length gas port .750" Gas Journal Package Contents: CMMG Inc 5.56x45mm Nato Mk4 Barrel Sub Assembly - 12.5inch Mr 4140cm Sbn 5.56mm Specifications for CMMG Inc 5.56x45mm NATO Barrel Sub-Assembly: Manufacturer: CMMG Caliber: 5.56x45mm NATO Threads per Inch: 1/2x28 Barrel Twist Rate: 1-7 Flutes: No Gun Model: AR-15 Included Accessories: Standard Condition: New Gun Type: Rifle Package Contents: CMMG Inc 5.56x45mm NATO Barrel Sub-Assembly What firearm models does the manufacturer say CMMG Inc 5.56x45mm NATO Barrel Sub-Assembly is compatible with? The manufacturer suggests that CMMG Inc 5.56x45mm NATO Barrel Sub-Assembly is compatible with AR-15CMMG Inc 55D470B: Barrel Sub-Assm 16.1in Light Taper Profile Salt Bath Nitride 1-7 Twist 5.56mm 1/2-28 Thread Mid Length .625in Gas Journal