I've got an M1A on order that I intend to hunt pigs with. It's pretty crucial that you be able to follow up quickly on those guys should your first shot not drop them.
I know a couple of guys that were out in the woods screwing around one weekend and got cornered by a large boar. It ran them into their pickup bed, but it couldn't make it up there itself. They proceeded to empty several magazines worth or 9mm and .40 S&W into it's skull and did absolutely no damage to it. They had to crawl into the cab of the truck through the split rear window and drive off. They came back the next day and couldn't find any sign that it was injured. There were a few drops of blood where the confrontation happened, but no trail.