loooong time ago I had to load for a belgium cape gun in 50-110 and 12 ga( cape gun because the rifle barrel was on the left side)maybe made for the colonial market once. it was not my gun and sold when the ammo project was ready. in this days I had to load in lathe turned NDFS brass from england if someone here still remember this.
12 ga brenneke slugs were loaded in magtech brass.
anyway, it was my only encounter with this cartridge that exist as a BP and a more powerful Nitro load.the case looks like an oversized .357 Mag case, not to big but big enough for anything.

http://thebiggamehuntingblog.com/2016/07/50-110-winchester/