George,
I've been looking at the pictures of your gun, and I can't really determine how it was headspaced. It is different enough from what I have seen over the years, that I would have a tough time without having it in my hands.
Up on the face of the breech are raised areas that project on to the base of the loaded cartridge. These are much more pronounced on a typical sliding breech gun that is equipped with them. These "obturator discs" do not seem to be a different part that is bolted in to the breech face on your gun, from what I can see, and they are, on a more conventional Darne gun.
The key sould go into final battery pretty firmly on a loaded gun. The adjustment is not on the barrels, they are an interference fit to the base that the breech slides on. If the key is sloppy at all in final battery with loaded cartridges in the gun, you might have an issue.
Nial, I once priced a V grade gun for a customer with R13 level engraving and wood.
It was never ordered or sold, but, it was possible to spec a gun for yourself through most of the Darne companies history.
It helped to be right there, with cash in hand, I imagine.
Best,
Ted
