Well if you are open to being convinced, a 500 gr cast bullet at 1300 fps will give you complete penetration on a ground squirrel.
I've found that a 250 gr Speer out of my .35 Whelen works well on ground squirrels.
I'm using a 200 grain cast in my 35 Whelen now. I've yet to take a deer with it, but it is the SHIZZ on chipmunks-- good penetration, and it makes a convincing crater.
Hint: put a pile of sunflower seeds underneath your 100 yard target stand.
