FAXON DUTY BBL 308WIN 18" RFL BGNRUpgrade your AR 10 platform with the Faxon Duty Series . 308 WIN 18" Big Gunner Rifle Barrel. This barrel offers an excellent balance between accuracy and maneuverability for your . 308 build. Machined from 4150 CMV steel and featuring a button rifled bore, this barrel provides exceptional precision and durability. The Big Gunner profile combines the best aspects of government and pencil profiles, offering improved harmonics and heat dissipation.