Yea I figured this out too. I shoot a 70 lb bow and I shoot a 358 grain arrow. My father shoots a 60 lb bow and shoots an arrow that is around 490 grains. When we shoot side by side in the same target his arrow go in deeper. I feel I have plenty of penetration for deer, but when i draw an elk tag there is no doubt in my mind i will be stepping up to a heavier arrow. That being said I think the lighter the poundage the heavier a arrow must be to get enough penetration.