I'm in Texas and have hunted pigs quite a bit. I've killed them with my bow (ground shot), a Ruger Model 1 in .25/06, 3.5" 12 gauge shotgun slugs, and, most recently, my Survivor .308. I won't be breaking ground here to repeat the mantra " it's about shot placement".
The .308 through the head at 100 yds killed it very dead, not so much as a twitch. I know people who kill them with .223 rounds with some regularity, but you better hit them in the ear hole or there abouts.
It is true that they can be very aggressive and can absorb a tremendous amount of abuse and keep moving. We have butchered some to find broadheads, shot pellets, and all kinds of wounds that would seem to have been fatal. Now anyone who has skinned a boar will tell you about the thick ( I've seen it more than 1" thick) mass of cartilage that covers their shoulders and about a third of their back.
While duck hunting I had one come to water about 10 yards from where I was standing, camoed and against a tree. I had 3" number 2 shot in the 12 gauge gun, but rather than hit it in the head I was too far back and caught him in the shoulder. He took the load without so much as a flinch, turned and stormed right at me. I didn't even have time to pump in another round. For some reason he got a couple of feet away, cut hard and ran back into the thick stuff. Maybe he couldn't make me out with the camo, tree background or whatever. He wouldn't have picked up any movement because I was locked-up scared.
Anyhow, they are a real scourge and cause millions in crop damage. Fun to hunt and excellent to eat. Go get 'em!