Does anybody happen to know for which gun this cartrde was intended for?
Just a wild guess here - repurposed rolling blocks originally in .43 Spanish?
Ole, can it be converted to take a round about 1mm larger in diameter than a 12GA ?
The Spanish license-made Springfield rifles used a breech block, hammer, and receiver that were about 1-1,5 mm wider than the M/1867 used in Norway with 12ga, so it’s very possible.
The Spanish also used a Peabody rifle in .43 but that seems less likely of a candidate.