Even the Great One gets things wrong sometimes…
There is no one single factor that is the most important in the field of terminal ballistics (other than, maybe, hitting the target…). Shape, size, and weight (actually, mass) of the projectile and its terminal speed (NOT the widely-quoted “muzzle velocity”), as well as location of impact are all factors of importance.
There most certainly IS a thing called “hydrostatic shock,” though I wouldn’t agree with the overall effects often attributed to the phenomenon. And contrary to the offhand comments of several posters, water and other liquids are most definitely compressible, though not as easily compressed as, say, air. It is this very compressibility, NOT the lack of it, that enables the pressure waves that comprise hydrostatic shock to exist in the first place. It also explains ripples in a pond, tidal waves, sonar, and a host of other things. But I digress…
Also, a bullet is not “red-hot” when it strikes a target, nor at any other point in its travel. Were this the case, the relatively soft metals most bullets are made of would melt, and the bullet would disintegrate shortly after leaving the muzzle.
Qadgop was kind enough to supply a comprehensive list of possible results of a gunshot wound that would cause death, but most of these can be classified in the general categories of tissue damage, blood loss, shock, and infection.
Clubs, maces, etc. are designed to kill or disable through damage by external impact, often relying on the victim’s own bones to supply penetration of internal organs or tissues. Edged weapons, such as swords, spears, knives, arrows, etc. are designed to kill or disable through penetration, causing organ damage, massive bleeding, or both. Bullets are designed to kill or disable through the delivery of a fairly large quantity of energy to a target, enabling it to wreak havoc randomly, in a number of ways. (I refer again to Qadgop’s list.)
Hunting bullets are carefully designed to maximize damage to a living target, primarily by insuring that the kinetic energy of the bullet is transferred as completely as possible to the target. Most military bullets are not so designed, partly because of the emphasis placed on penetration of armor, partly due to restrictions dictated by international conventions. Thus, while every M-16-toting grunt carries magazines full of full-metal-jacketed rounds, no hunter would be seen in the field packing FMJ’s. Enemy soldiers habitually hide in buildings, behind obstacles, in vehicles, etc. and the penetrating abilities of an FMJ bullet are often advantageous in battle. But you seldom see a whitetailed deer driving an armored personnel carrier; extreme penetrating power is not needed when hunting animals.
Gee, I’m windy sometimes!