I have killed about 120 of them and the problem is, if you are on the ground with them, that you may encounter one larger than 120 lbs, SO I would say that if you have a choice the 30-30 would be about the 'smallest' caliber I would suggest. I have killed them with 223, 30-30, 35 Rem (one of my favorites), 7-08, 308, 35 Whelen and shotgun slugs. Just use a heavy well built bullet if you anticipate an encounter with a BIG hog. You can always kill a little hog with a big gun, but it can be a problem trying to kill a big hog with a little gun!