The only and I mean only place to shoot a larger size hog with a .22 rimfire is the little hollow spot, kinda below the ear. I know it sounds crazy to hunt them with a .22, but thats the only way to do it, steel shot in a shotgun just doesnt cut it, I have shot a few with my bow, but they are few and far between becasue of the distance you must go to set up a stand. ATV's can only be used on marked trails and the hogs will be in one area one week and another part of the refuge another, they kinda roam with the food sources and hunting pressure.
As far as ammo, I use solid CCI maxi-mags. If I make the shot I should the hog will drop, and do the kickin chickin. If you dont or the angle is wrong you'll have to chase them. I'll only pull the trigger if the shot is good. So far I haven't lost one. Most of my buddies use either a semi-auto .22 mag such as the Ruger or Marlin, at least one uses a lever action. I bought a Ruger 77/22mag in target gray that I'm going to try this year, with the new pmc predator ammo. It's a semi-jacketed softpoint, pretty neat lookin.
Unless we are just looking for a trophy to hang on the wall, the smaller pigs are much easier to handle(100lbs or so) since you have to drag it out by hand, those big dudes are hard to get to camp or at least back to the trail were the ATV is....lol
Small pigs can be shot thru the heart/lung area if need be, the .22mag has enough juice to get thru the plate to the vitals....
Something that we see down here alot, mostly on the big bruisers, is the gristle plate behind the shoulder will have shotgun pellets, .22bullets and sometimes a broadhead in it. Thats why I feel the brain shot is the only one to take on a big boy.
Again, I may take heat from hunting such an animal with a .22mag, but its the only game in town for this area. And opening day there will be a couple hundred guys just like me doing the same thing.
Steve