The 6.5 x .257 versions are all smaller in diameter than the 6.5x55. I think the 6.5 x .257s came about as conversions for the 6.5 Jap.  Same potential problem as making 7.7 Jap from .30-06 cases.  They mostly got away with it in the 7.7 conversions because the rifle actions are strong.  I would not try to convert the .257 or '06 case for a Norse Krag.

There are a couple of larger European 6.5 cases, but would they function through the magazine?  Or did a Norse Ackley-son get his hands on the rifle?