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When Karl Dönitz announced Germany's resignation in May of 1945, surrendering German forces around Europe, the garrisoned forces in occupied Norway (mostly) did much the same. The war was over, and German soldiers and collaborators turned in their arms in droves.
Norway, once again free, looked at much of these armaments now in their possession and decided that this was some pretty good stuff, and they could plain take them as part of reparations, then issue it to their own rebuilding armed forces. Aside from many pistols, there were subguns which they didn't really have that many of before, admittedly in 9mm Luger, instead of their .45 Auto (Norway being one of the few countries outside of America which adopted the 1911 pistol and its large bore cartridge), but these were still good and usable, filling a purpose.
As well as those, there were machineguns, new and good ones, but they were in 7.92mm Mauser, not their standard 6.5mm Mauser. Looking at these machineguns, it probably was decided that they would be worth adopting, and then they would also adopt the K98k as their new rifle, slightly more modern than their Krag Jorgensen rifles, but more importantly sharing the same cartridge as the machineguns, and they had more than enough to rearm everyone.
At some point, the idea was investigated to transition towards the .30-06 Springfield cartridge, as they would be able to receive it as military aid from the United States in large quantities, and a few thousand K98k rifles were rebarreled for it, however it didn't go all that much further from there. Once NATO became a thing, the idea was floated to rebarrel these old Mausers to 7.62mm NATO for reservists, and a couple few thousand rifles were converted, yet again this didn't go much further, reservists seemed to just have been stuck with using the existing 7.92mm Mauser stockpiles.
These .30 caliber converted Mauser rifles are floating around in Scandinavia still to this day.