A long, long time ago, at a gun show in Hartford, CT, I bought a 19th century German percussion target pistol. It was missing its ramrod, and the action spring was too weak to work properly. I didn't know anyone who worked on antique guns and all this was long before the Internet, so it sat as an ornament all these years.
More recently, I bought at a provincial auction a 19th century revolver that was not described as out of order, but I found when it arrived that it would not hold cock. I finally found someone to work on these, and both guns are getting repaired.
The gunsmith measured the bore and told me the percussion pistol was .485, essentially .50 caliber -- 12mm in European parlance.
I was looking for comparison photos to provide ramrod examples, and I found a couple of similar percussion German target pistols on-line. Guess what? They were also 12mm.
This suggests to my mind that there must have been a 19th century German target pistol match category using these kinds of pistols in just that caliber. The trick is finding out anything about it. I was looking just now for German-language firearms forums without much luck.
Anybody here know anything?