Ask Ian: Why Didn't The M3 Grease Gun use Thompson Mags?
This "Ask Ian" episode from Forgotten Weapons delves into why the M3 Grease Gun and its successor, the M3A1, did not utilize the double-stack, double-feed magazines common to the Thompson submachine gun, despite the potential logistical simplification. The explanation centers on the M3's design lineage from the Sten gun, which employed a single-feed magazine due to its inexpensive, stamped construction. The Thompson's magazine retention system, featuring a T-shaped lug that required a substantial milled receiver for its track, was incompatible with the M3's simpler stamped receiver. The video also touches upon other US submachine guns like the M2 and UD-42 that did adopt Thompson magazines, but these also featured more robust, blocky receivers capable of accommodating the retention mechanism.












