Good to hear that you weren't seriously injured!
I would agree with the others about the double charge. I am paranoid about that happening so I try to make a habit of always looking down inside the case before placing a bullet into position. Also, I use Alan's Press Monitor to help make sure I haven't got distracted using my 550B. I go a little slower reloading than I could but I feel more confident that I am less likely to have a similar accident.
Also, thanks for sharing with us. You have reminded all of us that it could happen to anyone!
"Any man who thinks he can be happy and prosperous by letting the Government take care of him, better take a closer look at the American Indian." Henry Ford