m3 submachine gun
The M3 "Grease Gun" is a World War II-era .45 ACP submachine gun introduced by the US military as a less expensive substitute for the Thompson submachine guns, with most of its parts made of stamped metal. Entered service in 1943, the gun also saw service during the Korean War and Vietnam War.
Identifying details include a straight magazine well/foregrip, barrel with no sight post, cylindrical body, and retractable wire buttstock.