Not a double but flintlock: I had a mint---yes, mint---stamped 1800 on the stock Brown Bess that I used regularly for hunting and on the range until I sold it to a Connecticut antique dealer for $2,200. One of two found in an old New Brunswick barn, for which my father paid $25 each. Used it several weekends to spice up militia training with FNs. (Don't believe all stories about lousy accuracy.) Once, using too-generous powder covering ball in palm, the Brown Bess went straight-up from my hands about 15-18 inches and I caught it coming down---pure luck, all caught on 8mm Kodacolor.
off the corrosion topic- the accuracy reputation of the Brown Bess was due to the undersized ball load(often one ball and three buck shot)used by the military at the time
a tightly patch ball will often shoot very well out of a smooth bore-
