Hog Calibers & Kill shots

We started our hog huntin training with a guy here locally who has been doing it for years. He uses a knife for nearly every pig he takes. He had been trying to get us to hunt with him for several years, but listening to some of his stories about using a knife on the hogs I wasnt to sure it would be my type of hunting. I finally agreed to start going with him this year and it is a blast. I am still not into the knife for the simple reason I think it is more fun to use my .40 cal or 22 pistol. We hunt with dogs so it is much diferent than stand hunting. The only way to safely shoot a pig is once the dogs have him bayed you have to go up and drag the dogs off the pig, then have someone standing back a ways to take the shot once the pig runs a safe distance from the dogs. It is all about shot placement though. I have seen alot of pigs dropped on the spot with a good head shot from a 22, but I have seen several keep going with a bad shot from a 30-30