gjw,
one form of fraud/faking that I have seen is the use of a long dead famous name on a gun of a later period.One example that springs to mind was a very nice breech loading hammer gun engraved,Nock,Fleet Street London.Nock went out of business circa,1830!
There is currently a post on this forum seeking information on a breech loading gun by James Barlow of Litchfield, staffordshire, this may turn out to be a situation similar to the above?.

Roy Hebbes