Energy transfer[edit]
The energy transfer hypothesis states that for small arms in general, the more energy transferred to the target, the greater the stopping power. It postulates that the pressure wave exerted on soft tissues by the bullet's temporary cavity hits the nervous system with a jolt of shock and pain and thereby forces incapacitation.
Proponents of this theory contend that the incapacitation effect is similar to that seen in non-concussive blunt-force trauma events, such as a knock-out punch to the body, a football player "shaken up" as result of a hard tackle, or a hitter being struck by a
fastball. Pain in general has an inhibitory and weakening effect on the body, causing a person under physical stress to take a seat or even collapse. The force put on the body by the temporary cavity is
supersonic compression, like the lash of a whip. While the lash only affects a short line of tissue across the back of the victim, the temporary cavity affects a volume of tissue roughly the size and shape of a
football. Giving further credence to this theory is the support from the aforementioned effects of drugs on incapacitation.
Pain killers,
alcohol, and
PCP have all been known to decrease the effects of
nociception and increase a person's resistance to incapacitation,
[21] all while having no effect on blood loss.
Kinetic energy is a function of the bullet's mass and the square of its velocity. Generally speaking, it is the intention of the shooter to deliver an adequate amount of energy to the target via the projectiles. All else held equal, bullets that are light and fast tend to have more energy than those that are heavy and slow.
Over-penetration is detrimental to stopping power in regards to energy. This is because a bullet that passes through the target does not transfer all of its energy to the target. Lighter bullets tend to have more penetration in soft tissue and therefore are less likely to over-penetrate. Expanding bullets and other tip variations can increase the friction of the bullet through soft tissue, and/or allow internal ricochets off bone, therefore helping prevent over-penetration.
Non-penetrating projectiles can also possess stopping power and give support to the energy transfer hypothesis. Notable examples of projectiles designed to deliver stopping power without target penetration are
Flexible baton rounds (commonly known as "beanbag bullets") and the
rubber bullet, types of
reduced-lethality ammunition.
The force exerted by a projectile upon tissue is equal to the bullet's local rate of kinetic energy loss, with distance {\displaystyle \mathrm {d} E_{k}/\mathrm {d} x}
(the first derivative of the bullet's kinetic energy with respect to position). The ballistic pressure wave is proportional to this retarding force (Courtney and Courtney), and this retarding force is also the origin of both temporary cavitation and prompt damage (CE Peters).
Hydrostatic shock[edit]
Hydrostatic shock is a controversial theory of
terminal ballistics that states a penetrating projectile (such as a bullet) can produce a sonic pressure wave that causes "remote neural damage", "subtle damage in neural tissues" and/or "rapid incapacitating effects" in living targets. Proponents of the theory contend that damage to the brain from hydrostatic shock from a shot to the chest occurs in humans with most rifle cartridges and some higher-velocity handgun cartridges.
[18] Hydrostatic shock is not the shock from the temporary cavity itself, but rather the sonic pressure wave that radiates away from its edges through static soft tissue.
...
Big hole school[edit]
This school of thought says that the bigger the hole in the target the higher the rate of bleed-out and thus the higher the rate of the aforementioned "one shot stop". According to this theory, as the bullet does not pass entirely through the body, it incorporates the energy transfer and the overpenetration ideals. Those that support this theory cite the
.40 S&W round, arguing that it has a better ballistic profile than the .45 ACP, and more stopping power than a 9mm.[
citation needed]
The theory centers on the "permanent cavitation" element of a handgun wound. A big hole damages more tissue. It is therefore valid to a point, but penetration is also important, as a large bullet that does not penetrate will be less likely to strike vital blood vessels and blood-carrying organs such as the heart and liver, while a smaller bullet that penetrates deep enough to strike these organs or vessels will cause faster bleed-out through a smaller hole. The ideal may therefore be a combination; a large bullet that penetrates deeply, which can be achieved with a larger, slower non-expanding bullet, or a smaller, faster expanding bullet such as a hollow point.
In the extreme, a heavier bullet (which preserves momentum greater than a lighter bullet of the same caliber) may "overpenetrate", passing completely
through the target without expending all of its kinetic energy. So-called "overpenetration" is not an important consideration when it comes to wounding incapacitation or "stopping power", because: (a) while a lower
proportion of the bullet's energy is transferred to the target, a higher
absolute amount of energy is shed than in partial penetration, and (b) overpenetration creates an
exit wound.
Other contributing factors[edit]
As mentioned earlier, there are many factors, such as drug and alcohol levels within the body,
body mass index,
mental illness, motivation levels, body part strike (e.g., "armpit hold") which may determine which round will kill or at least catastrophically affect a target during any given situation.
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