The barrel isn’t split or damaged that I can see. If this was a severe over pressure that exploded the action the barrel would have split also. The action is the only thing that failed and it’s almost certain that it was from a brittle and cracked lug abutment. I personally had a M70 detonate like this action but it was from using the wrong powder. Both the barrel and the action split because the failure was from pressure that exceeded.....
This is a common misconception. A severe over-pressure will
not always split the barrel. In the example below the shooter filled the .257 Weatherby case with BlueDot and fired. One can clearly see that the barrel was not split. The rifle was a Weatherby Vanguard...
https://thefiringline.com/forums/showthread.php?t=341348&highlight=blue+dot.
