The .30-06 is great for medium game and long shots. As far as squirrels are concerned, there used to be a 55-grain sabot round that could be used to take small game as a varminter from squirrels to fox. The bullet that separated from the sabot was in the .23-.27 range. I believe it was Remington that made that round.
“Malo periculosam, libertatem quam quietam servitutem." (I prefer the tumult of liberty to the quiet of servitude.). Thomas Jefferson
"All that is necessary for the triumph of evil is that good men do nothing."
-Edmund Burke, Loosely translated from Thoughts on the Cause of Present Discontents. (1770)