This thread is about being more careful than you think you need to be.
I had my first-ever major reloading accident yesterday. In the middle of shooting a string of a fast high-round-count drill called Designated Target, my Shadow2 went Kaboom! I got a gas-blast in the face, and a couple of streaks of black on my hands--no injuries. The gun is also undamaged, except for a slightly bent slide stop, which is easily replaced. After 100's of thousands of safely loaded rounds, one bad one got past me.
What happened? My best explanation is a partial double-charge. I have been shooting 30-40k of 9mm per year, and this is the first time my QC has failed. I think know why it happened. I recently added a separate crimp station, which required taking out my RCBS Lockout Die, a mechanical sensor for powder level. A full double-charge (7.8gr) of PrimaV will just barely fit in a 9mm case, but the bullet won't seat, so I thought I was safe. Obviously that was wrong. My best guess is that somehow two unusually small charges dropped one after the other when I cleared a jam, and I didn't notice it. My Lockout die is now re-installed and tested. The separate crimp station isn't that important.
Take-home messages:
1. Rare events become exponentially more likely when the numbers get really large.
2. Safety procedures are best when they don't rely on human perception.
3. CZ Shadow2s are tough. A polymer gun, or a less overbuilt gun would almost certainly have been destroyed. Also the small, right facing ejection port probably saved me from a facefull of burning powder and metal fragments.
4. ??? what would you add?