STI Barrels are made from 416 rifle 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 6 lands and grooves. The barrels are vacuum heat treated and vacuum tempered to 40Rc, then machined to exacting specifications. The barrels are short chambered to allow the gunsmith to cut the chamber to their application. Available calibers: .355, 9mm, .38 Super, .400, .40 S W, .450, .45 ACP.