David,
Thanks for the Elsie photos! PM sent.
The J. Manton 8 gauge was likely made inn Belgium and proofed in Birmingham as was the practice at the time. Manton and Co. marked guns were British and among the finest of the flintlock era.
From:
http://thedales.org.uk/joseph-manton-shotgun-maker/
From SHOT-GUNS their History and Development – by Major Hugh B.C. Pollard 1925
"The best British makers towards the end of the eighteenth century were Egg and Twigg, but they were rapidly surpassed by the genius Joseph Manton, who was born in 1764 and died bankrupt in 1835, after an amazing career in which expensive litigation absorbed all his profits."
Threaded Mode