Looks like too much pressure and not an obstruction too me. It seems that screw hole was the thin spot that initiated the failure. If shooting the factory Remington Nitro 27 handicap loads shown, then that's too hot for an old gun. Considering the destruction shown, maybe they were reloads. I hope we find out.

The RST tent was right there selling proper loads. I hope he regrets saving a few bucks on shells.