Those certainly look like obstructional bulges. It is noted that when Bell intentionally burst a G grade Parker Damascus barrel by going up in the vicinity of 30K PSI it still burst in the chamber, actually between the chamber & the hole for the extractor leg. For those barrels to have bulged that far down if it was only from a regular shell there had to be an extremely thin weak area there. I believe you could "Bet the Farm" that it was some type of obstructional burst. Highly unusual to happen in both barrels, likely faulty reloads the shooter thought were low pressure. Probably had he shot regular factory "High Pressure" loads it would not have occurred.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra