This is a U.S. Model 1873 Springfield Trapdoor rifle (longer barrel than a carbine) which uses .45-70 "Government" cartridges. It was manufactured at Springfield Arsenal in 1881.

It is single-shot, loaded by opening the "trapdoor" breech cover. Under the front barrel is a ramrod (actually a cleaning rod), and a combination sling swivel and stacking swivel. It would have been issued to infantry or garrison troops, not cavalry, and possibly used during the Indian Wars or Spanish-American War.