Thanks gentlemen. Most of these questions will have to wait till I take delivery of the gun. The fully-rifled barrels are in the order of 20 inches, and the gun is fairly light, built for a 3-dram charge at most IMHO. At this stage I can only speculate on the cartridge for which it was chambered, probably 2 1/2 inch, round ball, paper case. We'll see soon enough!

Daryl: While I am prepared to concede that patch-boxes may have been fitted to a few very early breech-loaders, as a matter of 'tradition' at the time, the very thin chamber-walls are suggestive of cut-down tubes from an earlier piece. IMO it is not unlikely that both the barrels and the stock were once parts of a very nice 12-bore muzzle-loading rifle. We'll probably never know, and of course it matters not. Fun to speculate, though!

Tinker: If you visit without one of your 16-bores, you'll jolly-well be sent back home to get it!