[nobody_special]

First of all, you are a physicist. How many pounds of force does it take to break bone... especially when you take into account the small frontal surface area of a bullet. We are talking about 9mm and .357 Sig. Given that the shot is made perpendicular to the target (not a angled shot that may deflect) these are not going to be stopped by skin (unless you are a rhino) and will certainly destroy muscle tissue. If it breaks bone, that can cause secondary fragments in the body and increase the hemmoraging. This is what causes incapacitation and death rather than simply penetration. Many people have survived getting impaled or even shot by arrows.

Sure... and arrows do more damage than pistol rounds at close range, primarily due to the huge large arrowhead combined with tremendous mass (incredibly high momentum, thus good penetration against non-armored targets). Most people survive being shot by a pistol, too. My examples, that you are responding to here, were not regarding 9mm or .357 Sig; I was simply pointing out that energy alone is not the most important factor in the efficacy of terminal ballistcis.

Hemorrhaging on this scale is not a quick cause of incapacitation or death. It may be lethal, but it's not going to kill someone instantly. Even damage to the heart or a major artery (aorta, etc.) does not guarantee an instant kill - and the heart is a major organ!

Psychological effects (pain, surprise, an unwillingness to die) are much more likely to stop someone quickly than any injury short of direct CNS damage.

Go back to your fluid dynamics text books and imagine a massive amount of energy being deposited into your body. We are dealing with very high velocities here. Even dropping a pebble into a bocket of water causes ripples. Imagine that pellet being thrown at 1400 feet per second... and expanding as it enters.

The human body is not composed of fluid alone, and most non-fluid parts are remarkably elastic. Every bit of information I've read suggests that the permanent wound channel is the significant factor in handgun wounds, and hydrostatic shock is greatly overestimated as a mechanism of injury. (It's a bit different for rifle wounds, where the shock wave is many times stronger.)

Consider the energy in a 9mm round at 350 m/s and 8 g mass (124 grains, 1148 ft/s). That's 490 Joules of energy, but only 2.8 kg-m/s; relatively low momentum of course. A substantial fraction of that 490 J will not be dissipated by hydrostatic shock, but will instead do mechanical work directly on the target by breaking skin and tissue. The shock wave energy dissipation depends on the cross-sectional area, but the difference between ~0.7" for 9mm and ~0.8" for .45 isn't going to make a huge difference. Anyway, 490 J is probably comparable to the amount of energy transfered by a hard hit with a baseball bat (to within a factor of a few).

After reading up to this point, I will need to ask for your credentials and ask where the heck you studied physics. So you are basically saying that if a round does not strike a vital organ or CNS, it doesn't matter what size the bullet is? I guess that why physicist make horrible doctors. When you look at a wound channel from a FMJ and wound channel from a hollow point that properly expanded, do you notice a difference? The FMJ will punch through and usually leave the same size exit wound as the entrance wound. With a properly expanding hollow point, the exit wound is larger than the entrance wound, and not necessarily just the diameter of the expanded bullet (unless it has slowed down so much that it barely has enough energy to penetrate the body). This is because the energy from the round acts in a cone like pattern, from the nose of the bullet. The energy is not simply a vector (straight in straight out). That is also why you stretch cavities in ballistic gels rather than a simple hole straight in and straight out.

My credentials? B.S. from here; B.A./Ph.D. from one of the better UC's.

I'm not saying that the size of a round is completely unimportant; I am saying it's one of the least important factors, at least among the rounds we're discussing. The more important factors are having sufficient penetration, and good/lucky shot placement. Aside from there being little difference in ballistic gel performance between these rounds, my conclusion is also supported by (imperfect, but still relevant) statistical data, for example here.

And yes, if it doesn't hit a vital organ or CNS, it doesn't make much difference how big the hole is. A slightly larger bullet makes a slightly bigger hole, but a modest increase in the amount of bleeding does little to immediately stop an attacker. Besides, the amount of bleeding is really going to depend on whether or not a major artery was hit, which depends more on shot placement (or random chance, really) than bullet size.

I am not in the military so I should always worry about over penetration. More importantly, hollow points are much more effective at incapacitating someone than a FMJ. Ask any cop what he carres and I can gaurantee that you would be hard pressed to find a single one who carried fmj. How many bad guys do you encounter wearing body armor (unless you are talking about the LA bank robbery). Furthermore, shooting through cover is risky since you don't know what is on the other side. Besides, the chances of that are pretty slim too.

That's why I qualified my statement... it only seems relevant for the military.

Bottom line... Hollow Points are much more effective at incapacitating someone compared to FMJ (as long as there is suffucient penetration). The more powerful the round, the more energy is deposited into the person, even if it penetrates completely. The deceleration of the round while inside the body is where the force is transferred. Furthermore, there is some hydraulic shock (much more so with rifles) that creates a "splash" within the body and radiates out from the bullets path. This is what can shut down the CNS very quickly versus causing death through hemmoraging.

What makes you think that hydrostatic shock will shut down the CNS in a typical COM hit? The CNS is mostly in the cranium, and what isn't (the spinal cord) is reasonably well protected by the spinal column.