I think this is an excellent question. And, this is why I like to carry a .45 with the heaviest bullet possible.
All targets that I aim for when I have the option are surrounded by thick bone.
I aim for the chest, the head, and the pelvis, whichever one is the easiest target or needs the most attention.
I like the pelvis for followup shots because it will #1 impede their mobility (nothing is %100, but a broken pelvis is a good possibility of stopping someone) and #2 there is a lot of blood going around that area. A shot to the pelvis is likely to bleed somenoe out as fast a a shot to any other target with large blood vessels nearby, because it is all "hit and miss", nothing is for sure. The pelvis itself will bleed, and you have a high likelyhood of hitting an artery in that area, and the bone fragments may severe any arteries you miss, and lastly, the very structural damage along may STOP them. Seems like a pretty decent target to me, just about as likely to cause them to bleed out as any other target with lots of blood vessels.
COM is a good thing to go for, but if I have any time at all to even remotely aim, I am going for those three targets.
The liver shot is a big target, almost COM in most cases,a nd will kill but not STOP very well.
The best real STOPS seem to be severing a major artery, and that is pure LUCK. You can aim for the general area (chest, COM, pelvis) but it takes a little luck to actually hit a major blood vessel and STOP someone in short order.
For me, first comes the chest shot, and if that does not work, then body armor must be assumed, and a head shot or pelvis shot follows. The pelvis shot is safer and easier to make, and can be very effective against such an agressor. And hey, if that does not work, that is why I have more bullets in my gun
Let's also keep in mind that this is not the shooting range with silliouette targets. The guy probably is not going to be standing there facing you. Know your anatomy from all angles, and aim for the spot that gives the easiest target, and the most likelyhood of stopping them. This will be different in every case, which is why it is safe to just say "shoot for the largest mass you see".
Under real diress, I am just going to aim for the biggest target but if I have any time to aim I will be a little more selective.
With the heavy .45 I know that the momentum it carries will have the highest chance to penetrate through the chest or head and still leave a nice big hole, or break the pelvis and hopefully stop the attacker.
Of course, this is all just survival 101. If I really had time to aim ("like a sniper"), I might be more selective, but those are the biggest and most effective targets, while easiest to hit and cause a STOP, IMHO.
Lastly, there is no chance that we are all going to agree here. But, do to my medical background I know my human anatomy very well, and I know very well what it takes to stop somone, and those are my
personal preferred targets to STOP someone in a fast paced survival situation where you have to weigh out the size of the target, how likely it is you will be able to hit it, and your odds of hitting something vital by aiming at it.
NOTHING is %100, but some targets are a little better than others for increasing your odds of hitting something vital enough to stop an agressor.
Even with a perfectly placed shot through a large blood vessel, do not count on it physically stopping someone for a very long time (in "fight seconds").
Only a CNS hit is "%100" and even that is not %100.
You learn real quick, the more you study all of this, to just try to avoid running across the wrong person, because a handgun will not be enough to stop them fast enough.
Sorry for the rambling...
[This message has been edited by jdthaddeus (edited September 08, 2000).]