Proof Research AR Type Carbon Fiber Barrel 6.5 Grendel 18in 8 Twist .750 Gas Journal Diameter 5/8-24 Thread. With these by Proof Research you get increased barrel life extreme accuracy and superior durability all in one device. Also this Proof Research AR-Type Carbon Fiber Barrel is up to 64percent lighter than traditional steel barrels of similar contour and that's significant enough to boost your shot velocity by a factor of two. The stronger full length steel barrels will deliver much more reliable results as well but the carbon fiber barrel will save you a bundle on ammo. Also you can reuse these carbon fiber barrels for years to come so that you can pass them down to future generations. Pick up the Proof Research Carbon Fiber Barrel today to see how research-grade carbon fiber can improve your shooting game. Specifications for Proof Research AR-Type Carbon Fiber Barrel: Manufacturer: Proof Research Fabric/Material: Carbon Fiber Threads per Inch: 5/8x24 Gun Make: AR Platform Condition: New Features of Proof Research AR-Type Carbon Fiber Barrel Up to 64percent lighter than traditional steel barrels of similar contour. Package Contents: Proof Research AR-Type Carbon Fiber Barrel Proof Research 121665: AR Type Carbon Fiber Barrel 6.5 Grendel 18in 8 Twist .750 Gas Journal Diameter 5/8-24 Thread