We only have fox squirrels here. Where I grew up in S.C., we only had grays. Never noticed one as harder to skin than the other, but my observation is that fox squirrels take a lot less killing. Was always impressed by the grays will to live, saw several take a full charge of #6 shot and still just about get away.

My favored rifle for squirrels is a Savage 219 in .22 Hornet shooting cast. If I use a rimfire, my preference is my old Winchester 72A. Used an old 16 gauge quite a bit last Fall.