I do remember reading that the .17 caliber rounds penetrate deeper after defeating body armor, but that still wouldn't boost my confidence in the thing.
Exactly. The larger the caliber used, the higher the probability of hitting something vital and the less precision is needed on the shooter's part. Can you kill someone with a 1mm bullet at 2000fps?....sure, but your level of shot precision must be so good that it would be practically impossible to achieve fast incapacitation.
More from Handgun Wounding Factors and Effectiveness:
"Physiologically, no caliber or bullet is certain to incapacitate any individual unless the brain is hit. Psychologically, some individuals can be incapacitated by minor or small caliber wounds. Those individuals who are stimulated by fear, adrenaline, drugs, alcohol, and/or sheer will and survival determination may not be incapacitated even if mortally wounded.
The will to survive and to fight despite horrific damage to the body is commonplace on the battlefield, and on the street. Barring a hit to the brain, the only way to force incapacitation is to cause sufficient blood loss that the subject can no longer function, and that takes time. Even if the heart is instantly destroyed, there is sufficient oxygen in the brain to support full and complete voluntary action for 10-15 seconds.
Kinetic energy does not wound. Temporary cavity does not wound. The much discussed "shock" of bullet impact is a fable and "knock down" power is a myth. The critical element is penetration. The bullet must pass through the large, blood bearing organs and be of sufficient diameter to promote rapid bleeding. Penetration less than 12 inches is too little, and, in the words of two of the participants in the 1987 Wound Ballistics Workshop, "too little penetration will get you killed." Given desirable and reliable penetration, the only way to increase bullet effectiveness is to increase the severity of the wound by increasing the size of hole made by the bullet. Any bullet which will not penetrate through vital organs from less than optimal angles is not acceptable. Of those that will penetrate, the edge is always with the bigger bullet."
Here's some from Agent Patrick in "10mm Notes" briefing to the FBI:
"Shot placement is obviously critical, and our test criteria presume that the shot is placed in the vital area of the body which contains the brain, upper spinal cord, heart and aorta/vena cava. This area runs from just above the eyes to the diaphragm, and is about 4 inches wide. But, as our experience in Miami amply illustrates, shot placement is only the first part of the equation. Jerry Dove placed his shot perfectly. Bullet performance is critical to translate shot placement into an effective, incapacitating wound. If shot placement was all that mattered, we could arm all Agents with .22’s. Secondly, perfect shot placement may be difficult to attain in the stress and dynamics of a shooting incident. The larger calibers offer a “margin of error” in that where a smaller bullet may just miss the aorta, for example, the larger one in the same placement will damage it. A good example is killing a 400 pound pig with a .22, something commonly done on the farm.
If the shot placement is exactly right, the pig is instantly killed. If it is off less than an inch, the pig goes wild and the process of killing it becomes rather lengthy and involved, whereas a larger caliber would succeed with a larger margin of miss than an inch. (Larger calibers are not used because they ruin too much of the pig a consideration that does not come into play in a shooting incident and besides which, nobody is going to die if the pig is not instantly killed anyway. In shootings, just the opposite is true)"
A gun fight is often fast and furious. Your heart rate is almost 200bpm causing combat stress so that you get tunnel vision, you shake, your body dexterity is greatly dimenished, and sometimes you don't even see your sights. Expecting to get precision hits in such a situation isn't practical. The larger your caliber(provided that you shoot it well), the better your chances of hitting critical areas of your target when you cannot get those precise shots. Shot per shot a good 9mm JHP has roughly three times the wounding ability as the 5.7mm.
