I have had a 500 and a 470 double on me so fast it sounded like one shot..It is an experience thats hard to forget..In one case I was thrown from the bench and hit on the back of my head and the rear sight landed on top of my head and cut a nice gash there..I woke up in a puddle of blood, that one hurt badly...The other one raised the gun straight up and I lost it in my right hand but kept it in my left but I had to turn completely around and chase the damn thing a couple of steps to keep from dropping it!

Then expect to spend the next few weeks trying to get that normal flinch under control