http://www.gunbroker.com/Auction/ViewItem.asp?Item=136814807 . The hammer may be missing due to the fact it was used as a donor for use on another hammergun. A pic of the marks/stamps on underside of the barrels with the forend off the barrels and the barrels off the reciever would help narrow the date. The steel buttplate was used up to the 1880s and possibly early 1890s.

Kind Regards,

Raimey
rse