Dear Tim,

Thank you for contacting Mearto with your appraisal inquiry. My sincere apologies for the delay with the apprisal.

The presented object appears to be a US Springfield Model 1884 trapdoor rifle with a cal of 45-75. The Model 1873 was the fifth variation of the Allin trapdoor design, and was named for its hinged breechblock, which opened like a trapdoor. It was in service from 1873 to 1892 (Reserve use afterwards) and around 700.000 rifles were built.
This piece is in bad to medium condition and there is no serious damage visible in the images provided.
A fair market estimation would be between 300 to 600 USD.
This estimate is based on actual recent past recorded auction sales of comparable items. Retail "asking prices" can be higher and may vary.

With kind regards,
George