What is your purpose you want the gun for?
Hunting, target, plinking?
Some states do not recognize BP handguns for hunting because many do not generate what might be considered high enuff energy. Some states only allow long guns for BP for this reason.
You might want to consider a Ruger Old Army. Probably one of the strongest and most accurate BP handguns on the market. I have heard of the Ruger being used for deer hunting to around 50 yards. T/C used to make a gun called the Patriot. They don't make them anymore, but these single shot BP guns were supposed to be top of the line and very accurate. I had bought one three years ago to deer hunt with, after doing some research on the energy levels at 30 and 40 yards and talkingto some Game Wardens I found thatmy state does not recognize BP handguns as legal for deer.I see them on occasion on Gun Broker though.

Good luck
Hank