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My father recently gave me his stash of guns and among them was a Remington Sportsman 12ga semi-auto shotgun. It looks to be in fair condition, if not better.
The first two pictures you posted are of a Remington Model 14 or 141 rifle in .25 Remington. It has a repair code of EXX3 which means it was at Ilion for a repair of some sort in October 1951.
The bottom picture appears to be a Model 11/the "Sportsman" barrel but what is shown is just a bunch of inspector's marks. If the "Sportsman" serial number is 4535xx it would be a 12-gauge of September 1940 vintage.