Fishbone Airsoft does an interesting test of doing a gelatin penetration test with light and heavy BBs at high FPS... "This time I have decided to answer a question I have had on my mind for some time. And I know that plenty of players have been asking the same; what is actually happening when you changing light bb's? I always wondered if heavy bb's will cause less or more destruction despite loss of velocity.

There you go that's the answer for this question."