Dear Dave,

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 Webley Mark I top-break revolver with a caliber of 455. It was developed for the British Army to replace the Enfield MKI and MKII. It was introduced in 1887 and replaced 1894 with the modified MK II revolver.
This piece is in good condition and there is no serious damage visible in the images provided.
A fair market estimation would be between 450 to 800 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,
Georg