Observing the wound, I assume the puncture was done by a fragment and not gas. No burns can be seen.

From the picture, the wall thickness appears sufficient. The crimp probably opened correctly but when the barrels failed, the gasses went multi-directional, thus blowing the crimp backwards and melting it somewhat. If the powder charge was doubled, odds are that the case would have ruptured and burst closer to the head. My picture estimate would be metal failure. It must be remembered that barrel bursts can be caused by a conglomeration of problems. Too hot a primer, slightly more powder, loose base wad, heavier shot weight, etc.

I don't see a bulge that indicates a bore obstruction.

Just some thoughts.