ORIGINAL: quiksilver

So, I guess when you consider that, if you're shooting two otherwise identical arrows (same head, same speed, same weight, same friction coefficient on the shaft, same fletchings) - and arrow A is a lincoln log (diameter .5"), while Arrow B is pencil thin (diameter .3") - you're probably going to get better penetration with Arrow B, simply b/c the force is transferred over a smaller surface area.

Yes.

Same goes with broadheads. If you have two identical arrows (same speed, same weight, same fletchings, same diameter, same friction coefficient on the shaft) - and you put a 125 grain muzzy on shaft A,while on shaft B, you put a 125 grain mechanical head with a cutting diameter of 2.75" - you're bound to get much better penetration from arrow A (provided that the blades are the same thickness/sharpness).

Yes.

So, while a KE calculation is nice and handy, there are hiddenpenetration killers lurking (fat shafts, shafts that "drag" more than others once moving through the target, broadhead selection, etc..) Unfortunately, these are things that can't be easily quantified by a quick KE or Momentum calculation. Instead, we resort to field testing.

Yes.

Good post and good discussionthough.