Agreed. I shoot .303 British, so I've had plenty of blown cases due to the slack locking lugs (I neck size only now, works much better). Even a complete case rupture won't do much of anything with the bolt locked down (except of course requiring one to use a cleaning rod to get the front half of the brass out of the chamber when you have a complete head separation).
This sounds like a squib round lodged in the barrel. It's a shame, but if you're rapid firing (or don't hear the difference in the sound that a primer-only or low charge makes) it can be deadly. Happened once to a friend of mine with FACTORY ammo (admittedly it was pretty old). In that case nobody was hurt, but the rifle was a wreck.
I once had a 22 rimfire lodge in the barrel of a rifle. For some reason, the front half of the brass went with the slug, and caused it to jam half way down the barrel. The barrel swelled up, but didn't burst.