This Surgeon 1581 extra long, repeater action has .473" bolt face diameter to fit a .308 Winchester with a Remington style extractor. It has a .45" recoil lug, tactical bolt knob, 30 MOA 1913 picatinny rail, a 1-1/8x16 tenon thread that requires a 1.35" diameter barrel, a shrouded, side mounted bolt stop to prevent accidental release, and an anti-jam rail to prevent a round from lodging in the raceway.