The General Motors Guide Lamp M3 Grease Gun is a usa-made blowback submachine gun chambered in .45 ACP, introduced in 1942. Primary use: military, sport. Type: Submachine Gun Action: Blowback Caliber: .45 ACP Capacity: 25 Year introduced: 1942, USA Weight: 88 oz Overall length: 24" Status: Discontinued Military use: Yes Intended use: military, sport