How to ruin your tighty whitey

[Bfh_auto]

As the French say. "bu-MER". Or in this case, "boo-MER".
This seems to me, as many other commenters as the result of a projectile being lodged in the barrel very close (or at) the forcing cone. Might be a structural fault in the barrel, too.
Typically an overload in the ammunition will blow up the chamber - cylinder - area.

All that said, I would prefer a handgun blowup to a rifle blowup. Handguns - especially revolvers - explode radially and typically up away from the frame. Evan in autoloaders, seldom does anything come rearward. Not even slides.
Rifles are cuddled up next to one's very head and face. Explosions in rifles also are radial in direction (away from where the explosion occurs) but a lot nearer one's brain housing group.

I do not knowingly shoot unknown reloads. Of much anything. There are a few individuals who seem to be reliable and thoughtful enough to trust in the matter. I have known some individuals in my past NOT on that list.

Back to the subject, I would like to examine the wreckage or read a proper report of examination.

Yes to everything you said.
I had one revolver blow up. It just felt like a normal load. But the word noise and smoke said it wasn't.
There are tons of blown up muzzle loader and rifle pictures with grotesque injuries.

 

[cslinger]

My man didn’t even flinch!! . Run it back in slow motion. I mean damn, I flinched. Dude is a boss.