This is Lot #1236 in the upcoming December 2020 RIA Premier auction.
At the suggestion of Colonel J.C. Kelton (Assistant Adjutant-General, Military Division of the Pacific and Department of California), the US Army adopted a 20ga shotgun version of the Trapdoor Springfield in 1881. Built at a truly minimal cost using 1873 actions and condemned .58 caliber barrels bored out to .635 inch (20 gauge), these Model 1881 shotguns had only three new parts (extractor, front sight bead, and screw lug attached to the barrel).
A total of 1,376 were made by 1884, and two were issued to each infantry company stationed west of the Mississippi. The purpose was to give soldiers some recreation and also a way to add some fresh game to the rather stagnant rations of barracks life in the post-Civil-War western Army. They were very well liked, and remained in posts until at least 1900.