Prairie Dawgs
Many, many years ago, a friend of mine invited me out to Montana. The ranchers out there had a big problem with the prairie dogs, the livestock stepping in the holes in the ground and breaking legs, stuff like that. So the ranchers didn't mind the occasional person coming along with a .22 thereabouts and whacking a few of the ornery critters. So we took a couple of Ruger .22 pistols out and drove along the edges of the ranchers properties taking pot shots at the little furry critters. Face it - .22 rounds are cheap, guns are fun to shoot, so what better way to spend the afternoon having fun and helping out the ranchers. :boxing:
So I guess to answer your question - .22 long rifle in a semi-auto Ruger pistol.