STI barrels are made from 416R rife grade stainless steel billet forgings. The bore is gun drilled, button rifled, then air gauged to offer the most exacting size, and most consistent barrel available. The rifling is 1 in 16 twist and has six lands and grooves. The barrels are vacuum heat treated and vacuum tempered to 40 Rockwell, then machined to exacting specifications. The barrels are oversized in the hood and lower lugs for match fit accuracy and short chambered to allow gunsmiths to cut the chamber to 45 ACP. Wilson/Nowlin ramp cut required in frame to install this barrel.