exists in the central nervous system after a high-energy missile impact to an extremity. A high-frequency oscillating pressure wave with large amplitude and short duration was found in the brain after the extremity impact of a high-energy missile ..." Wang et al. observed significant damage in both the hypothalamus and hippocampus regions of the brain due to remote effects of the ballistic pressure wave. Caliber Handgun calibers are a frequently discussed and disputed factor in handgun effectiveness. It is generally agreed that most intermediate handgun calibers will yield similar terminal results if using modern, quality ammunition. Caliber selection often can be reduced to balancing a handgun's physical features; weapon size, magazine or cylinder capacity, recoil, and ease of use. These features are all largely determined by the cartridge that the weapon fires. A list of many handgun calibers can be found at List of handgun cartridges. One-shot stops The only scientifically proven and biologically possible way to guarantee instant incapacitation is through the destruction of the central nervous system or brain. This will usually cease all motor-related and voluntary actions. If the central nervous system is not damaged or destroyed, there will be no immediate, physiological incapacitation. Since a central nervous system hit is very difficult in a dynamic situation, some people will use expanding ammunition or larger calibers. These can increase the odds of striking a part of the central nervous system. For example, a popular caliber in the United States is .45 ACP. It is among the largest practical handgun calibers in use, featuring a diameter bullet. With well-made expanding ammunition, a .452 bullet often expands to .70 caliber or larger. With a 9 mm Luger cartridge, the normal .355 bullet may expand to .50 or larger. Theoretically, a larger caliber should cause slightly more dangerous wounds. However, the unpredictable and uncontrolled nature of handgun use outside a laboratory environment makes this difficult to determine. Other situations where a single shot stops an attacker are most likely psychologically based. The attacker may be surprised that their subject is armed, and could flee without ever being struck. Alternatively, an attacker may be frightened after being shot and decides to disengage rather than press the assault. See also Pistol-whipping References External links Ballistics By The Inch Relationship between barrel length and bullet velocity. Effectiveness Ballistics