Oh! So, that reminds me of a story.

Waiting in line to check in at the ENT for allergy stuff, notice a guy sitting in a chair with a gauze patch over one eye. He notices my shirt (I was going to work after this appointment) and we get to a little small talk. I tell him I work in the manufacturing department, and he asks if our repair group is open for doing repairs.

I tell him they are, look up the number on my phone and give it to him, and ask him what happened. He said he had a round in backwards and it went off, and some shrapnel hit him in the eye. (That's why he was there.)

Alarm bells are going off in my head, but I think I managed to maintain a good customer service outward appearance and tone, as I managed to get more info out of him:

Apparently he loaded the rounds into the magazine backwards, and that's how he managed to chamber one backwards. His idea of resolving the issue was to get something long and poke it down the muzzle to try to knock the round out of the chamber. He probably hit the primer while he was doing that, and that's what caused the ND.

The only thing I can figure is that he was using the wrong caliber. Like, whatever model he had, he was using a caliber smaller than what he should have been using.