Proof Research Terminus Apollo 6mm ARC Threaded Rifle Barrel Sendero 16.5 in 7.5 Twist Pxt 5/8-24 Thread 1.9 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 Terminus Apollo 6mm ARC Threaded Rifle Barrel: Manufacturer: Proof Research Color: Carbon Caliber: 6mm ARC Projectile Caliber: .243 Caliber Barrel Material: Stainless Steel Barrel Twist Rate: 1-7.5 Barrel Profile: Sendero Firearms Threads Per Inch: 5/8x24 Gun Make: Terminus Gun Model: Terminus Apollo Gun Type: Rifle Package Contents: Proof Research Terminus Apollo 6Arc Threaded Rifle Barrel What firearm models does the manufacturer say Proof Research Terminus Apollo 6mm ARC Threaded Rifle Barrel is compatible with? The manufacturer says that Proof Research Terminus Apollo 6mm ARC Threaded Rifle Barrel is compatible with Terminus ApolloProof Research 156452: Terminus Apollo 6mm ARC Threaded Rifle Barrel Sendero 16.5 in 7.5 Twist Pxt 5/8-24 Thread 1.9 Weight Carbon