Dan posted a great video a few days ago about an unintentional double tap that made it’s way to the interwebs. He talks about an unintentional double tap that he once experienced, and also what went wrong in the example video.
Long story short, the shooter’s finger remained tight on the trigger, depressing it again during the recoil. Which, by the way, was a lot. It’s a Smith & Wesson 500.
The other issue with this particular shooter is that he was trying this one-handed. I can’t speak for everyone, but it seems that he didn’t have a whole lot of experience with this firearm and as a result, sent two bullets down the barrel instead of the intended one.
With firearms like this one, the recoil can indeed place the barrel of the gun in your face (which is why two hands are recommended) and if another bullet is on it’s way down the barrel, well, you can see a potentially dangerous outcome.