Help finding builder

[skychief12]

I have a gun with backaction percussion locks nicely engraved, double octagon barrels swamped, .62 and .61 with front brass and rear steel sights. It has a shotgun style walnut stock with checkered wrist. A wood slider box with a seashell carving. The metal parts are steel, all stamped with the script number "12". The bottom of both barrel are also stamped "GCB" inside a circled, Also both have a very small stamped "dkva" or "bkva" (maybe hard to read) which are inverted from the other stampings. The right barrel is stamp with a script "A". I would like to know who made this gun or where to start looking. I assume it may have been a buck and ball gun originally.

[keweenaw]

You'll not be able to identify a maker for that piece.  The marks on the bottom of the barrels are barrel maker's marks, not gun builder's marks.  Somewhere European, not English, not Belgian as either would have had proof marks in that period.

Tom