Matchlock, sounds like you are talking about a cap and ball revolver there. I ran into the same situation several years ago. My solution was then, to file a narrow, shallow dovetail into the bbl. custom make up a sight, install into dovetail with a push in fit ( with fingers, and then solder the sight into the dovetail, I used regular silver solder at the time but there are several solder products available now that require less heat and hold real well. Those bbls are skinny for sure, but the is enough there for a shallow dovetail and not affect safety. yours hounddog