Several posts here seem to treat the Joseph Manton and John Manton firms interchangeably, which isn't correct.
The Locks are marked J. Manton and the barrel rib is engraved Fine Damascus Steel and it has London Proof marks on the barrels.
Is this really from the fabled Jos. Manton shop?
Obviously not. Possibly John, but certainly not Joseph. The Joseph Manton firm was long gone by the advent of the breechloader.
I have one near identical made by Wm Moore that I believe worked for Manton, so maybe he made it while at Manton.
Wrong Manton again. Moore worked for Joseph, not John, and was long, long gone from Manton by the advent of the breechloader.
Check the proof marks again. Mantons don't say J. Manton. They say Joseph Manton.
Again, wrong Manton. It couldn't be Joseph Manton to begin with and, late in it's run, the John Manton firm did use "J. Manton" on lesser quality guns.
Since Stallones says that the proof marks are London, and it does appear to be an early breechloader, the assumptions that the gun is Belgian or fake aren't on solid ground without further data. In this case, the photos are essentially worthless without including the barrel flats and water table.