The fact that big bore revolver cartridges with a good SWC or LBT work so well, yet produce so little kinetic energy should make folks question the validity of KE as a gauge of a cartridge's effectiveness. I guess too many believe the old horse hockey about energy and 'need' a simple answer to a very complex question.
Big Bore Bullet make big holes and this lets a lot of blood out and lot of air in quick and this is what kills any animal, regardless of their size
