you know this is the 10,3x60R the so called "Bündner Patrone". RWS brass is still available here 2,40 euro each https://www.wiederladen-alzey.de/de/10-3-x-60-r-rws-huelsen-neutrale-verpackung

this is since over 100 years the standard hunting cartridge in single shot rifles only in the swiss kanton Graubünden. this was and is a large rural area in switzerland and the idea behind this was to prevent well to do hunter outperform the local farmer hunter with new and expensive small bore caliber. so everyone hunting up to this day with a big bore and the old british 450-400 became a standard hunting rifle rifle caliber as the graubündner cartridge