M3

The M3 was an automatic, air-cooled blowback-operated weapon that fired from an open bolt. The M3 was chambered for the same .45 round fired by the Thompson submachine gun, but was cheaper to produce, and lighter, although contrary to popular belief it was far less accurate. Constructed of plain .060-in. thick sheet steel, the M3 receiver was stamped in two halves that were then welded together. The M3 was striker-fired, with a fixed firing pin contained inside the bolt. The bolt was drilled longitudinally to support two parallel guide rods, upon which were mounted twin return (recoil) springs. This configuration allowed for larger machining tolerances while providing operating clearance in the event of dust, sand, or mud ingress. The M3 featured a spring-loaded extractor which was housed inside the bolt head, while the ejector was located in the trigger group. Like the British Sten, time and expense was saved by cold-swaging the M3's barrel.