I downloaded the video and ran it through Adobe Premier. IF this is a fake, it's a very good one. You can watch and see there is no discernible break in the action. The shooter never moves from his spot, his shadow does not change, the location of the shotgun does not change, the background does not change.
The shot gun twists, ever so slightly in the frame just before you see the discharge at the muzzle.
The first four pictures are still frames taken right before the discharge, the remainder are from the slow motion portion of the video.
The remainder are from the slow motion portion, and you can see more of the discharge.
My feeling is this is for real, and this guy is VERY lucky to be alive.
HOLY ****
What would possess a person to even try that? You couldn't see anything down there anyways... Why? Putting aside the fact that you're breaking rules, what would be the benefit of looking down the muzzle when you have a suspected dud?