Proof Research 264 Caliber Non-Threaded Rifle Barrel Competition 26 in 7.5 Twist Pxt 7.12 Weight Silver. PXT - PROOF Exponential Twist - is a complete rethinking of conventional rifling geometry and twist progression engineered to reduce engraving force minimize throat erosion and create a smoother transition as the projectile engages the rifling. Specifications for Proof Research 264 Caliber Non-Threaded Rifle Barrel: Manufacturer: Proof Research Color: Silver Projectile Caliber: .264 Caliber Barrel Length: 26 in Barrel Profile: Competition Threads per Inch: Non Threaded Barrel Twist Rate: 1-7.5 Barrel Material: Stainless Steel Flutes: No Gun Make: Proof Research Weight: 7.12 lb Package Contents: Proof Research 264 Caliber Non-Threaded Rifle Barrel Proof Research 155097: 264 Caliber Non-Threaded Rifle Barrel Competition 26 in 7.5 Twist Pxt 7.12 Weight Silver