My air rifle loves aluminum cans!
I fill them with water and watch them EXPLODE with a well placed hollow point. It splits them from top to bottom, spalying the sides out 2"! Yes, that's almost as wide as the cans themselves.
In case you are wondering, its an RWS 48 (1100 fps). And yes, its very effective on squirrels, completely penetrating with the same hollowpoints. Only the base penetrates, the front is blown off leaving an effective cone-shaped projectile to go through.
It also did a number on a few opossum, braining them with eye-popping explosiveness.