I'd point out that, as serious as the powder contamination is, the larger mistake was getting two clear warning signs, and continuing without figuring out what the problem was. In fact, I would say that not finding the cause on disassembly should be a pretty clear sign to take a big step back. If it's not a mild overcharge, then it's really bad news--something like what happened, or a mal-adjusted scale or simply the wrong powder entirely.