Rosco Manufacturing Bloodline 5.56 NATO Barrel M4 11.5in Carbine 1-7 Twist 1/2x28 Thread Nitride Black. 56 (NATO) barrels are designed to meet the modern day carbine shooters requirements. We are a long way from our daddy's "Sporter" AR and those specs just won't cut it anymore. From properly managed dwell times for SBR's to running Suppressed or setting up a balanced patrol carbine Rosco has incorporated your needs into their engineering. Rosco has successfully accomplished this by picking the right twist rates gas port diameters and barrel materials according to the barrel they are making (not a lazy blanket method). They have also balanced input from their consumers and military end users in order to bring you the AR15 Barrels you need not just the one they want to sell you. Specifications for Rosco Manufacturing Bloodline 5.56 NATO Barrel: Manufacturer: Rosco Manufacturing Color: Black Finish: Nitride Fabric/Material: 4150 CMV Material Caliber: 5.56x45mm NATO Barrel Profile: M4 Threads per Inch: 1/2x28 Barrel Twist Rate: 1-7 Barrel Material: 4150 Chrome Moly Vanadium Flutes: No Gun Make: AR Platform Gun Model: M4 Condition: New Gas Block Journal Size-Length: 1.2 in Country of Origin: USA Gas System: Carbine Length Features of Rosco Manufacturing Bloodline Barrel M4 5.56 NATO Gas Block Size .750 Barrel Crown 11 Degree Package Contents: Rosco Manufacturing Bloodline Barrel M4 5.56 NATO What firearm models does the manufacturer say Rosco Manufacturing Bloodline 5.56 NATO Barrel is compatible with? The manufacturer suggests that Rosco Manufacturing Bloodline 5.56 NATO Barrel is compatible with M4Rosco Manufacturing BL-115-M4-556-7-C: Bloodline 5.56 NATO Barrel M4 11.5in Carbine 1-7 Twist 1/2x28 Thread Nitride Black