10ga Double SXS Black Powder Shotgun Identification and Value

[Gargoyle]

18mm for 12ga.
It looks to be an average quality gun in respectable condition. Bore condition will determine whether it is a shooter or not. Hopefully the bores are as good as the exterior.

So, this being a 10ga the 19mm makes sense. There's brown surface rust throughout the bores. No pitting I can see. Some Ballistol on a brush ought do the trick.