12 gauge shotgun for squirrel, which somebody says they want to eat, is not a reasonable recommendation. .410 if you have to use a shotgun, .22LR if you're a good shot or PAL-rated air rifle.
I don't think chipmunks are considered small game, are they? And some squirrels are considered fur-bearing, so there's that regulation.
I shot plenty of squirrels with a 12ga cylinder choke and target loads. It kills them on the spot with few or no visible injuries. Plenty left to eat.