I have always felt that bullet diameter, construction, and velocity are what make a bullet lethal.
-Take a .338 and 7mm bullet at the same speed and the amount of hydrostatic shock from the .338 will be greater along with the energy and wound channel.
-If both bullets are delivering the same energy the 7mm will probably be going faster and cause more shock.
-Arrows (slow) kill by blood loss because they cannot deliver shock like a bullet. A fast moving bullet in the same place will often drop the animal due to shock and then the bleedout occurs rapidly. My oldest son once shot an antelope in the neck Mel Brooks style, and chased it for miles. It got away. With a fast bullet it would not have taken a step.
-Energy dumping is great if you are hunting prairie dogs with bergers or VG's, but shock and tissue destruction are what kills. I have seen two different hunters shoot animals in the brisket just below the heart and both animals were DRT with zero blood loss. Shock from a high velocity projectile stopped the heart both times. The heart was swollen and blue. Wierd eh?
-Elk are not made of steel but a .222 will penetrate 1/4" plate at 200yds. wheras a 45-70 with more energy will not. A .45ACP can't even do it point blank.
-If energy dumping is so fantastic then why are solids used on large African game? Oooops, I hit the buffalo in the shoulder with my Berger bullet and dumped all the energy!
-Take a 180gr berger and 180gr partition and hit an elk in the front leg bone at 500yds and guess which one runs farther?
-put a small bullet hole through an animals heart and it quits working quickly. A lung with a small bullet hole can work pretty good for quite a while.
I think that everything you need to know about bullet lethality can be learned by watching slo-mo ballistic gelatin videos. This vid shows all of the components of bullet lethality in my opinion. Speed, shock, penetration and plenty of wasted energy! YouTube - Triple-Shock X-Bullet
Making a good shot always helps too.