The military procured lots of shotguns for aerial gunnery training. They would mount them in a cradle in a truck,take off driving with the instructor and trainnee in back and shoot targets on the move,learning how to lead etc etc. Imagine during the war due to shortages the Govt used any arms from anybody. Matter of fact I have about 15 paper shotgun shells from WW2 loaded with 6's.7.5 and 8 shot sizes. These case are stamped US on the bottom by the primer. You figure any fighting rounds would be double ought.
