Agree. I think penetration relies on simple momentum mass*velocity and the cross-section of projectile, but not so simple when it sheds part of its mass along the way. Given the same bullet design, the 165gr would have the same momentum as the 180gr@1,200 if it goes at 1,309fps. If more than 1,309fps then the 165ge would have more "mo" and likely to penetrate deeper, if other variables held constant. Then we get into the age-old discussion of whether it's momentum MV or it's energy 0.5*M*V*V .... At a minimum, we should have proof here, that penetration is not simply a function of the bullet mass. A more informative experiment would be using two bullet weights but same JFP, 165gr and 180gr. Design and Verify their speeds to have the same momentum, say 1,309fps and 1,200fps respectively. See what penetration tells us, about the momentum model or the energy model fits better. Remember, the 135gr@1,600 would have the same Mo as the 180@1,200 , as far as the momentum model is concerned. So if the Mo model holds for penetration, these two would have the same penetration ???