I have seen incidents like this about a dozen times over the years.

No powder is a more common one, but double charges of fast-burning propellants is asking for a disaster!! I have loaded for 40+ years now, and so far, have managed to escape either scenario personally [touch wood! :lol: ] But I have been religious about checking powder levels in all charged cases BEFORE seating bullets, and I do not use progressive presses, so maybe that is the reason. One small distraction can cause a hiccup, so it's good to be very attentive to what you are doing. Our hobby is generally a safe one, but is far from idiot-proof!! Regards, Eagleye.