Dear David,

Thank you for the additional images and your patience.

The presented object appears to be a percussion lock SxS double-barrel shotgun. This shotgun is marked by the producer Geo. Menkin. Sadly no additional information is given in reference literature or similar databases. This engraving could be also named the former owner. The lock and metal parts are decorated with etched scrollwork and hunting scenes. This firearm was made in the last third of the 19th century.
This piece is in medium condition and there is no serious damage visible in the images provided.
A fair market estimation would be between 100 to 300 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