Looking around, I think it is possibly a Danish variant of the Remington Model 67 Rolling Block cartridges originally made for a joint Swedish-Norwegian arms purchase a few years after our civil war, first in rimfire and later in centerfire. At 0.47" groove, the bullet diameter for the OP's casting is just over 11.9 mm. The original cartridge's bullet is bigger at 12.6 mm, but there is an "11.44 mm" variant in QuickLOAD's database with an actual bullet diameter of 0.469". It is called: "11,44×45,5R Rem Danish M/67". The rim and back of the case are a little narrow for the casting, but the original cartridge looks a little big for it. The QL database says the dimensions are based on an "old SFM drawing". I don't know what SFM stands for but it may refer to the Swedish military. I do know the Wikipedia entry on the larger original m.67 cartridge shows a drawing in linjers which are tenths of a Swedish inch or of a Norwegian inch, two units that were about 5.7% different from one another and which are which are about 28% and 21% bigger than an American inch, respectively. So there is room for unit conversion error in all this. Indeed, just multiplying by the difference in lengths and diameters between Swedish and Norwegian unit difference just about converts between the two original cartridges. I have no clue what a Danish inch may have been back then.
