I have seen deer taken with every "small" caliber you mentioned. They may be small, but they sure seem deadly. I consider the .222 and .223 to be on the small side for deer, but the .243, .257, 25-06, and .270? My uncle has had great success elk hunting with a .270.

Nice theory, Killer243! We all know how vicious those squirrels can be when you tick them off with an underpowered rifle.