It really depends upon WHICH Squirrels we're talking about here...
When I first started hunting "varmint" squirrels it was down along the central Cali coast range.
Those were big California Ground Squirrels (which we also have up here in Oregon and they call 'em "Gray Diggers")
I went on several "Squirrel Safaris" with friends in the Spring time down in Los Padres National Forest. We'd use our .22LRs and that would work pretty well. But a month later they'd get really spooky and you couldn't get any closer than 125 yards from them so we needed something "more".
My friend bought a .22 WMR and I bought a Ruger #3 in .22 Hornet topped with a 6X scope on it. (This was all before the .17 HMR came out).
Later, after moving up to Oregon, the .22 Hornet wasn't up to the task of shooting the "Sage Rats" that we have over in the desert. For that I got a Sako .222 HB with a 16X scope on it.
Later I expanded my varmint hunting selection adding a couple of Remington 40Xs, one in .223 and one in .220 Swift.
But recently, here close to home, I've discovered a cash of those pesky Gray Diggers, so I got the .22 Hornet out and I also have a T-C Contender Carbine in .17 HMR for my gal friend.
Either one of them works well, but that little .17HMR really gets the job done well.
You can see it here.

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