There's always a chance of crippling any game we shoot at, whether head shots or not. That's one reason we practice, to lower that chance. On squirrels, if you're taking head shots, it's just about guaranteed if you don't hit it in the head it's a clean miss. I like to aim just a bit behind and below the eye. There's a little more target there and anything that hits close is instantly fatal. On center mass shots a low shot could be just as ugly as an almost hit on the head. I'm confident we all strive to not do either.
I don't like my meat mangled or messy as the back is my favorite piece and the wife always eats the ribs first. Then we each take a front and rear leg apiece. She always fries two squirrels for a meal.
der Forester is right, it isn't easy, at least for me and evidently him. By insisting on head shots it puts the hunt back into hunting. I won't shoot at a squirrel outside 20 yards or so because beyond that distance my misses far exceed my hits. I prefer a solid rest and a still squirrel. With the preponderance of grays in my area that means you're gonna wait...and wait.......and wait for that perfect shot. It's worth it when it all comes together.
Our limit is 6 per day and I have, on two occasions in my life, taken a limit of head shot squirrels. One of those times it was with 6 shots but I was a lot younger and so were my eyes!! I doubt I'll ever do that again and if I do it will be good fortune.
I love to hunt deer and black bear but if I had to make a choice to hunt only one animal for the rest of my life that animal would be squirrels, hands down, no questions asked. Besides, squirrel is a heck of a lot better eating than either...there just ain't as much of it!
Vic