Those hammers are quite distinctive, and have a very "Greener" look about them.
There's some unusual patterns there, and it's unusual to see such contrast between the segments of the tubes. I have a W&C Scott single 10 with a similar thing - very clear circumferential line where the tube proper was butt welded to the breech section, and a clear lap weld in the breech section - all plain twist though in mine.
There's someone within the Guild who is or was collecting and researching James Rosier's life and work; Ben Thomas is his name, I think. It'd also be worth having Pete Smith, president, at Vintagers have a look at it; the next shoot is on at Greenvale, near Kilmore, on Sat 30th of this month.
I do love our original muzzle loader/damascus barrel regs; not that there's much to shoot at this season.
