STI Guardian in 45 ACP. The 45 ACP variant of the Guardian carry pistol. Built on the wider 45 ACP 2011 frame with a 4.0-inch barrel and dehorned carry profile. The 45 ACP Guardian was marketed toward shooters who wanted the 2011 platform's reliability and capacity in the 45 ACP caliber for duty carry. Type: Pistol Action: Semi-Automatic Caliber: 45 ACP Capacity: 14 Year introduced: 2005, USA Weight: 35 oz Overall length: 7.5" Status: Discontinued Intended use: Service, Duty, CCW