swedish bore rifle are something different from german and british guns.
husqvarna made the Mod 17 A cape gun and differnt rolling blocks for 28 , 24 and 20 bore cartridges. brass case length was 50mm and I can find anything that this was available from any firm. maybe a job for local gunmaker to cut german brass and also rauhfoss brass from norway.
this cartridge was a homemade only option.