Sons of Liberty Gun Works AR-15 Precision SPR 6mm ARC Threaded AR Barrel 14.5 inch SPR Mid Length 1-8 Twist 5/8x24 Phosphate Black. Optimized for accuracy the SPR contour and 5/8x24 threads at the muzzle are by no means lightweight but are built with accuracy in mind. The PRECISION series are 416R stainless steel black oxide coated barrels. These barrels are also polygonal rifled with a 3 groove 1:8 twist bore. Specifications for Sons of Liberty Gun Works AR-15 Precision SPR 6mm ARC Threaded AR Barrel: Manufacturer: Sons of Liberty Gun Works Color: Black Finish: Phosphate Fabric/Material: 416R Stainless Steel Caliber: 6mm ARC Barrel Profile: SPR Gas Block Journal Size-Diameter: .750 in Barrel Twist Rate: 1-8 Gun Make: AR Platform Gun Model: AR-15 Gun Type: Rifle Rifling Profile: 3-Groove Polygonal Firearms Threads Per Inch: 5/8x24 Package Contents: Sons of Liberty Gun Works AR-15 Precision SPR 6mm ARC Threaded AR Barrel What firearm models does the manufacturer say Sons of Liberty Gun Works AR-15 Precision SPR 6mm ARC Threaded AR Barrel is compatible with? The manufacturer suggests that Sons of Liberty Gun Works AR-15 Precision SPR 6mm ARC Threaded AR Barrel is compatible with AR-15Sons of Liberty Gun Works 14.5Precision-SPR-6ARC: AR-15 Precision SPR 6mm ARC Threaded AR Barrel 14.5 inch SPR Mid Length 1-8 Twist 5/8x24 Phosphate Black