[270WINCHESTER]

Need some wisdom to try and clarify my confusion here. So for the most part it seems that people agree that heavier arrows will result in greater penetration then lighter arrows. correct? If so here is what I am now confused with. I was shooting two arrows side by side. Both VAP TKO's, same length both shooting 100-grain points. One set a 300 spine the other a 400. The 400 spine arrows had a total weight of 386 grains. The 300 spine arrows a total weight of 486 (the additional 100 grains came from inserts. So in theory the heavier 300 spine arrows should have greater penetration correct? However, from 30 yards they were just barely poking through a new block target, while the lighter 400 spine arrows were a good 2 inches through. So why is the lighter arrow getting greater penetration? The difference in the spine shouldn't have that much effect, or does it?
I'm shooting a PSE xpedite, 29" draw at 60lb . Not a slow bow by any means and from what I have heard from others and researched myself a 300 spine arrows seem more along the correct lines then a 400. Does 400 not seem under spined for this setup or??

Any advice on the subject would be greatly appreciated.

Thanks!