Sorry just a quick guess. Looks like a British East India company, lion holding a crown mark, with proof and inspector marks.
With a swivel ramrod and a circle for a lanyard, it is almost certainly one made for their sea service.
The East India Company, "John Company", controlled vast areas of India until the 1856 Indian Mutiny* and had what was their own navy. After 1856, the Brits took over.
Dave
* Apologies to members from India as they probably have a different name for that.
Not stating it's the case here because I don't know, but be careful of replicas coming out of Afganistan.
Reference books I have call it an East India Cavalry pistol Model 1820 made for native cavalry units from 1820-40. Produced in England and Belgium for the East India Company. If Belgium made, proof marks are under the breech, English marks are on the side of the barrel and should have both "V" (view) and "P" (proof) marks. Usually sell in the $400-750 range depending on condition and maker
Thank you all very much.
John