That early it most likely was chambered for the 2 5/8 inch 10-gauge brass shells. From the 1880 UMC catalogue --
Note they offered brass shells No. 10, to 2 5/8 inches, for .12, .15 or .16 1/2 each depending on primer, while brass No. 10, extra long, to 3 inches, were .15, .18, or .19 1/2 each.
From the 1887 UMC catalogue --
The 10-gauge 2 5/8 inch brass shell was pretty much the "standard" 10-gauge shell during the 1880s but with factory loaded paper shells and smokeless powder loaded shells coming on strong in the 1890s, the 2 7/8 inch seemed to win out as the "standard" 10-gauge length for loaded shells. But 2 5/8 inch NPEs both brass and paper were offered well into the 1900s. Rem - UMC was still offering brass 10-gauge 2 5/8 inch NPEs after The Great War.
Threaded Mode