Sorry to stick my oar in, so late in the discussion, but nobody asked if the locking lug of the bolt had been checked to see if there was any crack evident between the locking lug and the bolt. This was a single locking lug action, and had a reputation for extreme smoothness, but not great strength. It was not uncommon for a gunsmith to lap the locking lug so that the safety lug/guide would rest against the receiver to strengthen the action when a sporter was being built. The headspace would be adjusted accordingly. I wouldn't expect this modification in an unaltered firearm. Without magna-fluxing the bolt, the usual method to look for cracks in a receiver or bolt was to wipe it down with a gasoline soaked rag. The gasoline would evaporate off the body, but would still be evident in any crack.

As an aside, isn't the field gauge for the 30-40 Kragicon and 303 Britishicon the same?