Soldato
Squib loads are even scarier than a hang fire when they happen to inexperienced shooters or during rapid fire drills when even veteran shooters might not notice a different in report and recoil.
Yup, or you forget to put the powder in the load when hand loading your own ammunition, the primer typically has enough force to get the round half way up the barrel, obviously there is a big difference, but if your don't notice and put another round up you've got a problem.
If your lucky the barrel will bulge, and it'll ruin your gun, if your unlucky the pressure will go back and blow parts of the back of the gun towards your face/neck.
It very nearly happened to me when I hadn't been shooting for that long, I was using a knackered old Ruger 10/22 the thing wasn't great and wasn't unusual for a miss feed, but a fired a round and felt really weird, was almost going to think nothing of it until I saw this white granulated stuff on the bench, looked a bit like sugar, then realised that was powder, and sure enough the round had only half gone off. The range officer at the time was pretty grateful that I had noticed.
Not quite the same but same principle applies - a guy on a YouTube channel, Kentucky Ballistics (I'll link below) but he had a dodgy round which was 4 times over pressure, it blew the back of the rifle out into his neck and basically it's a miracle he survived.