This U.S. Model 1873 Springfield Trapdoor Carbine was manufactured and inspected at Springfield Arsenal in 1882.
It is single-shot, using .45-70 "Government" cartridges, loaded one at a time by opening the breech "trapdoor" -- thus the name Trapdoor. It has a compartment in the stock butt that contains a three-part cleaning rod and a broken-shell extractor tool.
Carbines were typically used by cavalry or mounted soldiers, primarily during the Indian Wars of the late 1800s. This is the gun issued to Gen. George Custer's ill-fated cavalry troops and used in The Battle of the Little Big Horn.