Rainier Arms Select 5.56 NATO Barrel 18in 1-7 Twist 1/2x28 Black Medium. They are able to reach our goal by sourcing a very high end barrel blank at an affordable price. They start off using a high precision match blank in 1:7 twist use a 5 groove polygonal rifling machine it to the highest quality you have a barrel that is the best value hands down in the industry. Specifications for Rainier Arms AR Select 5.56 NATO Barrel: Manufacturer: Rainier Arms Color: Black Fabric/Material: Stainless Steel Caliber: 5.56x45mm NATO Barrel Profile: M4 Gas Block Journal Size-Diameter: .750 in Threads per Inch: 1/2x28 Barrel Twist Rate: 1-7 Gun Make: AR Platform Gun Model: AR-15 Condition: New Package Contents: Rainier Arms Select 5.56 NATO Barrel What firearm models does the manufacturer say Rainier Arms AR Select 5.56 NATO Barrel is compatible with? The manufacturer suggests that Rainier Arms AR Select 5.56 NATO Barrel is compatible with AR-15Rainier Arms RAB-SEL-556-18-R-NF-BLK: Select 5.56 NATO Barrel 18in 1-7 Twist 1/2x28 Black Medium