On the subject of ‘stopping power’, One must realize that the various theories have very partisan adherants, many such adherants are religious in their ferver. This is not too surprising when one remembers that these men are trusting their lives with the choice they’ve made. Under those conditions you must believe you’ve made the best possible choice…
Now: RII, or Relative Incapacitation Index, has been largely discreditied, as has “Stopping” or “Knockdown” power. Real-world shooting results have the advantage of empiricism, but they’re clouded by the myriad factors involved in a human gunfight, including the psychological state of the combatants. Further, real-world shootings simple enough to even begin to decipher are relatively uncommon.
Still, these results do serve as a semi-useful backstop for theory. Dr. Martin Fackler, himself quite partisan, seems to have the best handle on the “whys and wherefores” of bullet function. To date, the best, most workable theory indicates that, barring a CNS hit, it’s the size (depth and volume) of the perminant wound channel that is the most reliable indicator of rapid bullet lethality. Essentially, a handgun bullet must be able to reach it’s target, penetrate that target, and then perform work inside the target, in the form of tearing and disrupting tissue and bone. Bullets don’t cut, they crush. They crush deep holes, dislocating tissue, tearing organs, muscle, and bone apart. Fast bullets tend to create large temporary wound cavities, but unless they hit a bone and redistribute their energy by way of secondary fragments, or hit relatively solid tissue (like the liver), the large temporary cavities don’t contribute much towards lethality, and represent much ‘wasted’ energy. Slow bullets tend create small perminant cavities and small temporary cavities, and further, tend to not create secondary fragments if they strike bone. Medium velocity bullets tend to create larger perminant cavities than slow bullets, and tend to ‘waste’ less energy than fast bullets.
All other factors being equal, the larger the bullet, the larger the perminant wound cavity. This can be achieved by using large fat bullets, or bullets that expand, or a mix of the two.
In general, any handgun bullet larger than about .35 inches, moving at a velocities larger than 800fps can be counted as a fairly reliably lethal bullet. Of course this is greatly simplified, and totally leaves out such factors as bullet shape, expansion, and bullet placement (to name just a few factors).
Rifle bullets are another story entirely…
To start, they have so much energy, in many cases, that they can turn temporary wound cavities into perminant cavities by the mechanism of stretching flesh so far that it tears. Not all rifles can do this, mind you, and even those that can do so, don’t always actually do so. Next, rifle bullets tend to be heavier (in most cases - not always!) than handgun bullets, and almost always are moving very fast, so tend to do greater amounts of work inside their victim. Rifle bullets, if so designed, also expand more reliably, and to greater extents than pistol bullets. Often, rifle bullets actually breakup and send fragments throught the body, even if that wasn’t the design intent. German 7.62mm NATO and American 5.56mm NATO are particularly notorious for this.
Also, IRT “Caliber”, there is another use… In Naval guns, a “caliber” designation after a bore diameter listing tells you how long the weapon’s barrel is, in multiples of the bore diameter.
Ex: 16", 45 caliber gun (US “Colorado” class battleship) would have a barrel 45*16" long, or 720 inches, or 60 feet long.