Proof Research Defiance Ruckus 6mm ARC Threaded Rifle Barrel Sendero 20 in 7.5 Twist Pxt 5/8-24 Thread 2.15 Weight Carbon. 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 Defiance Ruckus 6mm ARC Threaded Rifle Barrel: Manufacturer: Proof Research Caliber: 6mm ARC Barrel Twist Rate: 1-7.5 Firearms Threads Per Inch: 5/8x24 Gun Make: Defiance Machine Gun Model: Defiance Ruckus Gun Type: Rifle Package Contents: Proof Research Defiance Ruckus 6Arc Threaded Rifle Barrel What firearm models does the manufacturer say Proof Research Defiance Ruckus 6mm ARC Threaded Rifle Barrel is compatible with? The manufacturer suggests that Proof Research Defiance Ruckus 6mm ARC Threaded Rifle Barrel is compatible with Defiance RuckusProof Research 157374: Defiance Ruckus 6mm ARC Threaded Rifle Barrel Sendero 20 in 7.5 Twist Pxt 5/8-24 Thread 2.15 Weight Carbon