I just inherited several old muzzleloaders from my grandfather's estate. One that has me puzzled is a muzzleoading percussion double labeled Chas Osbourne. It's in pretty reasonable shape considering its age (which I'm not sure of).
It has a small amount of engraving, really nice checkering and the words "Fine London Twist" on the barrel. Does anyone have any knowledge about this gun? It also came with a battered "leg of mutton" case.

From G Boothroyd in Sidelocks and Boxlocks.
"Charles Osborne of Birmingham was a large and well known firm founded in 1838..."
Quick synopsis:
By the 1880s they'd moved to Edinburgh and had a shop in London. An 1889 catalog shows they still made muzzle loading shotguns at that late date as well as modern guns and rifles. Also made punt guns and were famous for whaling harppons
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I'm puzzled by your reference to a leg o mutton case. Those were usually for break-open guns, but you say this is a muzzle loader, which was rarely of break-open design. Can you post a picture?

The case doesn't belong with the gun. Sorry, my mistake. There were several other old guns in various states of disrepair in the lot. The Chas Osbourne is the only one in operable condition. Thanks for the info that is the most I've gotten so far.
Some of the others include an underlever shotgun that is so rusted I can't tell the make. There is another percussion double, a Winchester 1890 .22, and an extremely ornate stock from a flintlock with a large amount of engraving on the furniture and the patchbox.
Since they are all family pieces I'm going to have a lot of fun researching them.