22LR penetrates the skull with ease. I don't know why you think they wouldn't. With a 22, you have to aim for the brain between the ear and eye. On very small pigs, it sometimes can brake the vertebrae and drop the pig in it's tracks but if it's a good size pig, you have to shoot for the brain. Vital shots can also sometimes take out young pigs but are not reliable.

The 22mag is the minimum legal cartridge when hunting with the use of dogs here in Hawaii. With more power and slightly larger bullet, it should be able to drop a pig in it's tracks if you hit the spine or vertebrae. I don't know how it would work with vital shots but I'm sure it would be better than the 22lr.

Any cartridge from .223 on up can take out a pig. But pigs are the toughest animal around in my opinion. They are much tougher than elk. Good shots will kill them just as easily as any other animal but their ability to survive marginal hits makes them one of the toughest animals around. But any bullet that hit's them in the "Drop them in their tracks" area will drop them in their tracks. The vitals are a different story. I've heard some bad stories about the 30-30 but then, I've heard alot of good stories too. I would say that the minimum would be a .270 or 7mm. 300 win mag is a good bullet choice. So is 30.06. The bigger, the better for vital shots. 44mag. I prefer 12 gauge slugs. They punch a nice hole even through the thickest pad ensureing a good blood trail. Buck shot works good too at extremly close distance and is good if your driving the pigs with dogs because you can easily hit running pigs. The only bad thing is that you might hit the tusks.

The pad is actually a thick layer of dence skin. Notice how tough even thin skin is. Now imagine skin that is 1 - 2 inches thick. You can shoot low in the chest at the heart and go completely under the worst of it ensureing a great blood trail.