Theory #2. The "hydrostatic shock" theory is (and always has been) in serious doubt...the evidence is by no means conclusive. In fact, this theory has been largely discredited. Bullet wounds also do NOT "knock an animal off it's feet"...unless it's a 20mm explosive shell, for example. Death occurs from blood loss and the onset of cardiovascular "shock"....(i.e., bleeding out, either external or internal).... it does not occur just from tissue damage, unless the tissue damage is so severe as to cause immediate collapse of the circulatory or nervous systems (the 20mm shell, or something similar, as mentioned before)... or the loss or severing of some vital organ (picture a high-explosive shell blowing off the head, for instance - thus severing the brain from the body). Frangible bullets, in terms of "immediate put-down" of game, or any other living target, are not as effective as those causing the "theory #2" type of damage, especially for medium to large game (or even humans, for that matter). Frangible bullets are best used for headshots, at close range...i.e., assassinations, things of that nature.... or particularly small game, such as those animals used as targets for "varmint hunting".