Scientific Evidence for "Hydrostatic Shock"

by Michael Courtney, PhD, Ballistics Testing Group
and Amy Courtney, PhD, United States Military Academy

The entire paper is very understandable and is well worth reading. Some interesting quotes:

Debates between bullets that are “light and fast” vs. “slow and heavy” often refer to “hydrostatic shock," which describes remote wounding and incapacitating effects in living targets in addition to tissue crushed by direct bullet impact. Considerable evidence shows that “hydrostatic shock" can produce remote neural damage and rapid incapacitation.
Recommendations

The FBI recommends that loads intended for self-defense and law enforcement applications meet a minimum penetration requirement of 12” in ballistic gelatin.[8] Maximizing ballistic pressure wave effects requires transferring maximum energy in a penetration distance that meets this requirement. In addition, bullets that fragment and meet minimum penetration requirements generate higher pressure waves than bullets which do not fragment. Understanding the potential benefits of remote ballistic pressure wave effects leads us to favor loads with at least 500 ft-lbs of energy.

With a handgun, no wounding mechanism can be relied on to produce incapacitation 100% of the time within the short span of most gunfights. Selecting a good self-defense load is only a small part of surviving a gunfight. You have to hit an attacker to hurt him, and you need a good plan for surviving until your hits take effect. Get good training, practice regularly, learn to use cover, and pray that you will never have a lethal force encounter armed only with a handgun.