The Colt M3A1 Grease Gun is a usa-made full-auto submachine gun chambered in .45 ACP, introduced in 1944. Primary use: military. Type: Submachine Gun Action: Full-Auto Caliber: .45 ACP Capacity: 30 Year introduced: 1944, USA Weight: 88 oz Overall length: 24" Status: Discontinued Intended use: military