ORIGINAL: bigcountry
Eldeguello in responce to your post, let me point you to Newtons laws also. Equal and opposite reaction is used to a point here too. Not true that 5000ft-lbs would they a deer 50ft. For that assertion, no energy would be used or lost with the crushing of the bullet. No energy would be lost entering or penetrating the deer. The deer would have to be infinately hard and so would the bullet. Misusing physics just a tad here. You won't believe how much energy is lost just from the deformation of the bullet. Try a test. Get two pool balls, and smack one against another at rest. See the distance moved. Now put a 1/4 cotton on the one to smack it, do the same thing. Enormous amount of energy lost. Also pool balls are close to ideal as a person can reasonably get. If they were infinately hard, the effect would be ten fold as they deform also.
You are right, of course! The factors you mention are all involved. That's why the "foot-pounds" business is so meaningless in determining killing power! It's HOW THE ENERGY IS USED that determines what happens when a living thing is shot, rather than HOW MUCH ENERGY THERE IS, as calculated by some arcane formula.!!