This term is used as a more-or-less informal measure of the power of a weapon and is generally used in the context of small arms. It does not necessarily refer to whether or not the weapon can kill someone, but rather the weapon's ability to incapacitate or otherwise render immobile the target. Generally, the idea is that a weapon with good stopping power, when fired at an oncoming attacker, will knock his ass on the ground.

Stopping power is derived from the kinetic energy the weapon is able to impart to the target. For instance, a 9-mm pistol fires small bullets at a relatively low speed. It is about as effective as a paintball gun against, say, a couple of bank robbers in full body armor. On the opposite end of the spectrum, an M-16 fires relatively large caliber bullets at a very high speed. If these don't succeed in penetration, they still have enough kinetic energy to put the guy down on the ground, giving you a tremendous advantage in whatever it is you're trying to do, like reading his gas meter or selling him encyclopedias.

"Stopping power" is a supposed measure of a particular cartridge's ability to produce one shot stops. A term popularized by Marshall and Sanow who compiled information and did a rather flawed study on street shootings. They took the type of ammunition used, (caliber, bullet type, bullet weight) and made a rather inaccurate index of "stopping power".

To achieve immediate physiological incapacitation, not neccesarily death, on a human target a projectile must meet one or more of the following requirements. Note that the psychological shock of being shot is enough to stop some people but should not be relied upon.

  • Vital Central Nervous System (CNS) damage, this leads to paralysis and therefore incapacitation.
  • Rapid blood loss, usually brought about by big gaping holes made by big bullets or small but rapidly expanding bullets traveling at high velocities (1200++ fps). Rapid meaning in the order of deciliters per second.
  • The Hydro Static shock delivered by a tremendous amount of energy transfered.

Of the three, it is only the CNS hit that can guarantee immediate incapacitation. Blood loss is second and the third does not seem to be a reliable method of incapacitating an attacker as handgun or even rifle rounds simply do not have the energy to produce incapacitation by hydro static shock on targets as big as homo sapiens. This hydro static shock has only been seen in rifle rounds hitting small targets like varmints.

Marshall and Sanow are from the light and fast school. They believe, probably because of their findings from their flawed studies, that a light projectile travelling at high velocities (like the 9mmx19) is preferable over a big and slow projectile (like the .45 ACP). Thompson and LaGarde are of the opposite opinion, which is one reason the 1911 was chambered in .45 ACP.

Arguing the merits of both schools of thought will get you nowhere and will quickly become a chaotic debate over temporary crush cavities, permanent crush cavities, stopping power index, and all other such highly technical and acedemic (sometimes arbitrary) matters.

There is only one absolute truth in this debate however, faster AND bigger (heavier) is always better. It is when you substitute one for the other that it gets confusing.


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