If it is Karlsborg, with a 41 date (Not Code), then it can only be Norwegian 7,9x61 Browning MG, made under German Occupation.
The Germans utilised the Norwegian Brownings as Anti-Aircraft Guns on the Reichsbahn during the Invasion of Russia.(I have Photos).
If it is Swedish, then it is 8x63 M1932 MG cartridge, and a 41 date would be correct for Swedish production.
Look at the length of the Neck of the Cartridge case…It is too short for a .30/06. Check the based(head) measurement…both the 7,9x61 and the 8x63 are around the .480-.490" diameters, with a Rebated Rim at .470/.475
PS, I thought Karlsborg was Norwegian, not Swedish??? I may be Confused.
The Crown definitely looks Swedish, and the Layout is Swedish, so the 8x63 Description is more likel;y correct.
Must be the Cardiac Meds…