Let me relate a personal experience to you for a moment. I have worked at a meat packing plant for 6 years now, and during that time, have had the opportunity to try different guns/ calibers on the cattle/hogs that we slaughter. These animals are enclosed in a metal cage we call a knock box, and shots are taken at no more than 3-4 foot. I once tried to dispatch a steer with a 9mm with hardball ammo. I shot it 3 times in the head, before I gave up....the cow just shook off the hits, and stayed standing. Granted, I'm talking about an animal that is 1200 lbs, yet after doing many(autopsys) of the heads(as in cutting horns off, etc....), the skull on the forehead of a beef is no more than 1/4" thick, give or take a little. Add to that, the skin, which is about the same thickness, and you get my point....no more than 1/2" to penetrate! Would using defensive ammo have downed the cow with one shot?....maybe, but after much shooting, and reading on law enforcement tests of bullets, shots taken into a hard medium(i.e. bone/metal/wood), the bullets usually don't expand much if at all. I ended up finishing the steer off with a .22lr rifle, because it is the perfect combination of cost to penetration for such a close range affair. If you want my opinion, I would say to get a 22 handgun for targets, and if you want to hunt for boar, get a large caliber revolver for hunting. Granted, you can do what you want, but I wouldn't trust my leg to a 9mm!!! Just my $.02.
~~~Cattleskinner