FredC wrote on May 19^th, 2015 at 1:35pm:

Butlersrangers, that Swiss blowup kind of messes with my theory. It would be interesting to see a high speed video of each of the blow ups. After the high pressure event they are not coming apart as I would have expected. Just a couple of notes on the US Krag I just rebarreled: The bolt did have a lot of over travel with no case in the chamber. If this is the same with a 6.5X55, the bolt could follow a severely resized case way to far. The chamber was .010 to .012 larger than an unfired case.  Not sure if this was from an oversize reamer when the gun was first assembled or if the barrel swelled with use over the last century. If it swelled with the relatively low pressure loads then the  barrel steel is fairly soft.

The steel on Norwegian Krags is like the steel used in SE Mausers.  It was probably some of the best in the world at that time.