The Faxon Duty Series, Gunner Big Bore Contour Barrel for the AR-15 458 SOCOM is manufactured 100% in-house from cradle-to-grave. The barrel is machined from certified 4150 mil-spec bar stock steel with nitride coating for added durability and longevity. Each barrel is magnetic particle inspected (MPI) to ensure perfect surfaces and sub-surfaces as well as air-gauge tested to ensure superior accuracy. The Faxon Gunner Big Bore is button rifled and includes the Big Bore barrel extension to guarantee control of this giant round! Features4150 CMV ConstructionSalt Bath Nitride FinishBig Bore Barrel ExtensionPolished 11-degree Target CrownParticle InspectedButton Rifled