I have seen hogs dropped with everything from a .22lr to 12ga. I do feel better with a larger caliber but the 5.56mm placed right will do a number too. I have a friend who put 18 rds of 5.56mm into a big hog, followed up by 25 rds of .40S&W for good measure--oh yeah, that was on top of a .243 Win that a friend of his put into it first.
5.56mm placed multiple times works great. I think it was designed to be shot multiple times.
