I agree with Susquatch. Most of the time you can drop them if you hit them right with a .22, but I"ve had too many get up and run off when we shot them with a small caliber gun. We hunt them at night a lot and when you flip the light on you don't have a lot of time to shot so you don't always have time to take careful aim and try to shot them in the head. We end up shooting a lot of ours behind the shoulder and I've seen several of them we shot that had several scars from being shot in the shoulder where it didn't kill them. Now I shoot them with a .450 Marlin. I've crawled through the brush too many times after shooting one before and having it get up and run off. We can normally find them but it is not much fun crawling through brush on your hands and knees after a pissed off boar. We've had them run after being shot with everything from a .223 to a .300 WM. If you shot them with a small caliber bullet in the shoulder the shield on a large boar can stop the bullet or have the wound close over making it hard to track. When we shot one with my .450 there is a large hole and plenty of blood to follow though we've never had any run more than a few yards after shooting one with it.