The design of the M1A1 along with the redesign of many other parts for faster production had reduced the time required to manufacture an M1A1 by 10.11 hours over the earlier M1928A1 model.Д®arly M1A1s were equipped with many parts that were originally manufactured for use on the 1928 and M1928A1 Thompson. All of the parts specified had been redesigned to require less labor hours in their manufacture. These parts shall not conform to said government specification but to the Savage, Auto-Ordnance or United States drawing number placed after the part nameвЂќ. The contract specified вЂњSavage agrees to manufacture said guns in accordance with the United States Government specifications which are identified as AXS-725 (revision 3) dated 7 January 1943 except each of the following parts are to be incorporated in the gun. In 1943, Auto-Ordnance ordered from the Savage Arms Corporation under contract G-19, 100,000 Thompson Submachine Guns M42-M1A1 type without magazines, slings or other accessories.

The M1A1 Thompson was formally approved at an Ordnance Committee meeting held on 29 October 1942. It was also noted that the bolts with and without the fixed firing pin were interchangeable. In order to distinguish between submachine guns equipped with separate firing pins and fixed firing pins, the submachine guns fitted with the fixed firing pin would be designated as Gun, Submachine, Caliber. The Springfield Ordnance District was notified that manufacture of a fixed firing pin bolt for use in the M1 submachine gun was authorized. It was also noted that the fixed pin design saved considerable manufacturing time and that the bolt was strengthened by elimination of the deep drilling operation necessary to accommodate the firing pin and spring. Tests at Aberdeen indicated that the M1 submachine gun equipped with a fixed firing pin functioned slightly better than the standard M1 submachine gun. The four parts were eliminated from the design by making the firing pin an integral part of the bolt. In September of 1942, Aberdeen Proving Ground was instructed to test вЂњA modified version of the M1 submachine gun, that eliminated the firing pin, firing pin spring, the hammer and hammer pinвЂќ. Less than 100 M42s were produced before the вЂњfixedвЂќ separate firing pin was completely eliminated and replaced by a projection machined directly on the bolt face. The firing pin, spring, hammer, and hammer pin were omitted.

The firing pin was fixed in an extended or вЂњin batteryвЂќ position. The prototype M42 was originally fitted with an M1 bolt with a separate firing pin, but the pin was secured in the bolt in a manner that made it a non-moveable part. The Savage Arms Corporation, who originally developed the M1 version of the Thompson, had continued attempts to further simplify the design by experimenting with a fixed firing pin model they designated as the M42. The Thompson Submachine Gun ID Guide, Part VII: The M1A1 Thompson Submachine Gun

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