If I were to use a Shotgun on Hogs, I would use Slugs.
A large Hog, has a Shield, and very thick skull.
No, skulls on hogs are not "very thick," not even on large ones. In fact, much of the skull is going to be thinner than that of a human skull. They may have a small brain box relative to the overall size of the head and slope and angles that enhance deflection of bullets and so getting to the brain may pose some issues, but it isn't because the skull is particularly thick.
This video (warning for language and imagery) is of the sort that helps promote the notion of super hog skulls. The video claims the bullet bounced off the head. You get the impression than almost none of the shots are entering the hog because the guy keeps shooting and the hog remains alive though he is shooting at the hog's head.
If you look closely, the "bullet" that "bounced" off the pig's head was just the jacket. Jackets are sometimes stripped off the lead when they enter or pass through harder materials. So the bullet entered, but without the jacket. The bullet did not bounce off.
The first and second shots generate much less physical impact movement of the pig than the third shot. Why? There is no damage to the face or head of the pig from the first couple of shots. Why?
Well maybe because the first shot actually hits the downed tree first. It appears to continue on and hit the back of the pig. The second shot appears to pass between the pig and the ground, below the pig's left ear. In other words, the shot doesn't hit the pig solidly either.
The third shot is supposed to be into the pig's eye. Yet the closeup at the end shows that at 3-4 feet, the shot clearly missed the pig's eye. However, the pig was significantly impacted by the third shot.
Conclusion? The shooter is a crappy shot. The first shot went through wood first, likely stripping the jacket off, and impacting the pig as fragments, not as a solid slug. The second shot doesn't actually impact the pig directly and likely missed below the pig. The third shot does directly impact the pig and the pig is finally put out of its misery, but the shooter clearly missed his stated target.
http://www.youtube.com/watch?v=rI0l29YGA-c&feature=related