I will be the oddball in the group and say that when I was a "serious" squirrel hunter I used a 10-22 with an aftermarket bull barrel and CCI Stingers. This was back when I kept squirrel dogs and hunted often. I used the 10-22 especially on the trips when I hunted alone. My thinking was that if the dogs treed the squirrel they deserved the chance to retrieve the squirrel, and I thought the Stingers gave me the best chance of making that happen.
When they treed a squirrel in big longleaf pine, it was a real challenge to spot him, and when I was alone it was a real challenge to shoot him even after he was spotted. The squirrel would often swap sides of the tree or limb when I moved, and many times getting a head shot was impossible. The good thing about the Stingers was that you could hit the squirrel almost anywhere and knock him out of the tree, and if he hit the ground he belonged to the dogs.
The Stingers were also not as inaccurate as many would think in that particular gun. It didn't have a match chamber, and I've heard that they will often shoot better in a gun that doesn't have a tight chamber. I bought that barrel because others told me it would shoot them, and it will consistently shoot 10 shot groups under an inch at 50 yards. That won't win matches, but they would do an amazing job of killing squirrels even on marginal hits.
But I usually hunted with a group of folks and I would carry my 10" Contender. It shot Winchester Power Points better than Stingers. I usually didn't take the shot anyway if I had a group, and I always got one guy to carry a shotgun to get any runners or to get one that a rifle missed.
My dogs all got old and died and I don't have one now. I miss having them. Most of them were Treeing Feist, but my best dog was half Feist and half Rat Terrier. Since he wasn't pure bred, the field trial guys didn't want him and I got for $100. Blake was the best bargain I ever got in my life.
