Popped more than a few tree rats with my .220 Swifts loaded with 55gr VMax's smoking out an average of 3720fps. Head shot equals removal of head
Body shot equals a fairly large greasy stain on the tree and a tail
Ya want overkill, hit one with a .22-250 loaded with a 40gr VMAX flying at a cruising speed of around 4250
Those buggers will even skin the tail out for ya! Pink mist! Was out smacking ground hogs and this little bugger was irritating me! Bang, POOF, no more irritation
As to the OP, I've killed thousands of squirrels with both solids and HP's. Whatever my rifle liked to eat is what I went with. Stick either one in an ear hole and watch it drop.