I said it before but I feel the need to say it again. I keep my inspection of "duds" to an absolute minimum, which means none at all.
The example of a round going off in the BAR's breech as it was being extracted after failure is evidence. Imagine if there was an additional 2-second delay, and the operator removed the round by hand? Instead of scattering the receiver it would have sprayed the firing line with bits of bone and tendon, not to mention shards of brass and hot gasses to the face and eyes. Put a few feet between you and the same explosive and you might get a few cuts or minor burn, but you're going home in the same number of pieces you arrived in.
My point is, eye-f'ing a dented cartridge case doesn't improve your shooting, and won't reveal mysteries about the inner-workings your firearm. Unexploded ordnance, even something as small as a .22LR, is a coiled viper. Treat it with proper respect at all times.
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Not a failure/hangfire, but a quick story to give some insight in the energy in propellant, which is lower than that in high explosive. I don't know all the details but I know the basics, hopefully I get it fairly accurate. Guy was disassembling an artillery shell, about to remove the fuze from the case. The fuze has several safeties, including a magnetic/inertial safety that physically breaks the explosive train, and is only is disengaged as the round spins in flight, so it is quite safe on the static-protected bench.
He's using a screwdriver to remove retaining screws and BOOM, there's an small explosion. The screwdriver is embeded through the guy's hand, fingers lacerated. He's alive, thankfully the fuze and the main charge didn't go off.
So, what happened?
It was believed that in storage, minute traces of explosive material had migrated into the threads where the screw was inserted. As the screw was turned out of the hole, those specs of HE became trapped, compressed and sheared until there was enough pressure to set them off in a very confined space. That much energy in a volume smaller than a pin head should always be feared, even if you've worked on/around it for 30 years. The day it doesn't scare you is the day you put yourself and those around you at risk.
Be safe.