The heavier ball will penetrate deeper. It is exactly why the early hunters used 4 and 8 bores for African game, instead of Tennessee squirrel guns.
There are some things that simply don't follow a mathematical pattern, and this is one of them.
“Nine-tenths of tactics are certain, and taught in books: but the irrational tenth is like the kingfisher flashing across the pool, and that is the test of generals. It can only be ensured by instinct, sharpened by thought practicing the stroke so often that at the crisis it is as natural as a reflex.” ~ T. E. Lawrence