The Antique Firearms dealer who sold this beautiful relic to me said that it was dated to 1830-1840, and that it was most likely a North American made long gun.
The barrel is 20 inches long and it's got an 18 gauge(.637")Bore.
I imagine this was made by modifying an older musket.
The short barrel makes it more manageable for someone on horseback
There was no actual providence or history known about this Muzzleloader, and so an educated hypothesis is necessary.