The M3 (and its followup improved M3A1 model) was the United States' answer to the high cost and manufacturing complexity of the Thompson submachine gun. The M3 "Grease Gun" (because really, that is what it looks like) was a very inexpensive weapon with a stamped and welded receiver and only a fed milled parts. It also had the slowest rate of fire of any World War 2 submachine gun at about 450 rounds/minute. Its weight, compactness, and controllability made it almost universally preferred over the Thompson, at least by soldiers who had to carry and fight with either of them.
The Grease Gun is reputedly extremely controllable because of its low rate of fire, but this is my first time to actually try shooting one. Will it live up to that reputation?
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