If you want a cap and ball revolver in .50 caliber I'm afraid you'll have to look for an antique one. I believe some of english percussion revolvers were larger bore than there American counterparts. Some of these were well over .50 caliber. I suppose you could probably have a currently manufactured revolver modified to take a .50 caliber ball, but that would be expensive, Bowen could probably do this on a Ruger Old Army.
I thoroughly disapprove of duels. I consider them unwise and I know they are dangerous. Also, sinful. If a man should challenge me, I would take him kindly and forgivingly by the hand and lead him to a quiet retired spot and kill him.
- Mark Twain