While in no way wishing to sound like a wet blanket, I have to wonder: is it possible that this is one of the much-dreaded "Khyber Pass Guns" manufactured in North Pakistan/South Afghanistan? From the pics the quality of the finish looks good - what I've read on the subject leads me to expect a fairly dodgy finish from a lot of these pieces, including the inclusions of a fair tonnage of black-brown filling material - but the mixture of dates, proof marks et al makes me think somewhat along those lines. Stylistically, in fact, I'd suggest (and expect to be corrected having done so by the experts hereabouts) that it bears quite a striking resemblance to the British Heavy Dragoon pistol of the mid-18th century (see
http://www.firearmscollector.com/ima...0110%20018.jpg for instance). Anyway, just the twopenn'orth of a newbie.
Meredydd Jones