Did I miss something in the pics? How did you determine .32 cal? Looks as if you could well be right, but just wanted to know how you knew??

False muzzle and appears to have the true Whitworth octagonal rifling system. That would put it sometime after ~1860 or so, but it could have been built much more recently. I would guess about 1885...

Whitworth bore with a percussion action that looks more like a Tryon. Given the false muzzle, I would think it was intended more as a target rifle than a hunting gun. Have you measure that barrel across the flats? Rifle's weight?

http://www.eldreds.lotfind.com/catal...&ord=1&row=501 has a listing for a combo rifle/shotgun by the same maker. Perhaps someone at that aution house could help you with valuation.