Some years ago I posted some of these but I’ve acquired a lot more since then and thought you all may like to see some!
Wilhelm Collath invented a shotshell variation that had a small pin that rested in a percussion cap half an inch into the case. The wider centerfire hammer would hit the pin which knocked it into the cap to set it off. The reasoning was to make the ignition travel backwards first so that it would have a little more time to burn the powder before building up the pressure to propel the shot. This allowed for less burning powder to travel down the barrel.
He also came up with his own size numbering system. They roughly equate like this:
0 -> 10g
1 -> 12g
3 -> 14g
4 -> 16g
5 -> 18g
6 -> 20g
7 -> 24g
8 -> 28g
As shown in the picture, they were also, but not commonly, made in a couple of the regular English gauges.