Rainier Arms Select 300BLK Barrel 16in 1-7 Twist 5/8x24 Black Medium. We are able to reach our goal by sourcing a very high end barrel blank at an affordable price. We start off using a high precision match blank in 1:7 twist use a 5 groove polygonal rifling machine it to the highest quality and matched with our limited-life time warranty you have a barrel that is the best value hands down in the industry. Specifications for Rainier Arms AR Select 300BLK Barrel: Manufacturer: Rainier Arms Color: Black Finish: Nitride Fabric/Material: Stainless Steel Caliber: .300 AAC Blackout Barrel Length: 16 in Barrel Profile: M4 Gas Block Journal Size-Diameter: .750 in Threads per Inch: 5/8x24 Barrel Twist Rate: 1-7 Flutes: No Gun Make: AR Platform Gun Model: AR-15 Package Contents: Rainier Arms Select 300BLK Barrel What firearm models does the manufacturer say Rainier Arms AR Select 300BLK Barrel is compatible with? The manufacturer says that Rainier Arms AR Select 300BLK Barrel is compatible with AR-15Rainier Arms RAB-SEL-300-16-P-NF-BLK: Select 300BLK Barrel 16in 1-7 Twist 5/8x24 Black Medium