The Thompson M1927 Thompson .45 ACP is a usa-made semi-automatic submachine gun chambered in .45 ACP, introduced in 1927. Primary use: self_defense, sport. Type: Submachine Gun Action: Semi-Automatic Caliber: .45 ACP Capacity: 20 Year introduced: 1927, USA Weight: 88 oz Overall length: 24" Status: Discontinued Intended use: self_defense, sport