[Frank Ettin]

Originally Posted by Brian Pfleuger

...Hydro-static shock is not "knock down power". It is a shockwave that passes through the in-compressible fluids in the body and disrupts/damages the NERVES, mainly, in the various tissues. Any remote damage (ruptures) in the tissue is a result of pressure waves in an closed space (a "bag of water", essentially). For instance, I have seen a deer's heart torn open even though the bullet remained intact, wasn't within several inches of the heart and there was no wound channel (such as from bone) leading to the heart. This is from the pressure wave. It's the same effect that blows a milk jug to bits even though the bullet only hits a tiny spot.

While disrupting the nerves or rupturing the heart may very well cause the target to drop on the spot, it is not the same as the force of the bullet directly "knocking down" the target.

Handguns, certainly those typically carried for SD can not reach the velocities required for hydro-static shock, ...

Correct. In general, velocity must be in excess of 2,000 fps for hydrostatic shock to be a factor.

At the velocity of most self defense handgun cartridges, hydrostatic shock is too negligible.

Originally Posted by robert1811

...However, incapacitating a targets CNS will lead to them dropping dead on the ground. Hydrostatic shock can do this...

No it can not -- at least unless one is using a cartridge firing a bullet at a velocity considerably in excess of the velocity of most self defense handgun cartridges.

Let's consider how shooting someone will actually cause him to stop what he's doing.

1. The goal is to stop the assailant.
   
   
2. There are four ways in which shooting someone stops him:
   
   
   1. psychological -- "I'm shot, it hurts, I don't want to get shot any more."
      
      
   2. massive blood loss depriving the muscles and brain of oxygen and thus significantly impairing their ability to function
      
      
   3. breaking major skeletal support structures
      
      
   4. damaging the central nervous system.
   
   Depending on someone just giving up because he's been shot is iffy. Probably most fights are stopped that way, but some aren't; and there are no guarantees.
   
   Breaking major skeletal structures can quickly impair mobility. But if the assailant has a gun, he can still shoot. And it will take a reasonably powerful round to reliably penetrate and break a large bone, like the pelvis.
   
   Hits to the central nervous system are sure and quick, but the CNS presents a small and uncertain target. And sometimes significant penetration will be needed to reach it.
   
   The most common and sure physiological way in which shooting someone stops him is blood loss -- depriving the brain and muscles of oxygen and nutrients, thus impairing the ability of the brain and muscles to function. Blood loss is facilitated by (1) large holes causing tissue damage; (2) getting the holes in the right places to damage major blood vessels or blood bearing organs; and (3) adequate penetration to get those holes into the blood vessels and organs which are fairly deep in the body. The problem is that blood loss takes time. People have continued to fight effectively when gravely, even mortally, wounded. So things that can speed up blood loss, more holes, bigger holes, better placed holes, etc., help.
   
   So as a rule of thumb --
   
   
   • More holes are better than fewer holes.
     
     
   • Larger holes are better than smaller holes.
     
     
   • Holes in the right places are better than holes in the wrong places.
     
     
   • Holes that are deep enough are better than holes that aren't.
     
     
   • There are no magic bullets.
   
   
3. With regard to the issue of psychological stops see
   
   
   • this study by Greg Ellifritz.
     
     As Ellifritz note in his discussion of his "failure to incapacitate" data (emphasis added):

     Originally Posted by Greg Ellifritz

     
     ...Take a look at two numbers: the percentage of people who did not stop (no matter how many rounds were fired into them) and the one-shot-stop percentage. The lower caliber rounds (.22, .25, .32) had a failure rate that was roughly double that of the higher caliber rounds. The one-shot-stop percentage (where I considered all hits, anywhere on the body) trended generally higher as the round gets more powerful. This tells us a couple of things...
     
     In a certain (fairly high) percentage of shootings, people stop their aggressive actions after being hit with one round regardless of caliber or shot placement. These people are likely NOT physically incapacitated by the bullet. They just don't want to be shot anymore and give up! Call it a psychological stop if you will. Any bullet or caliber combination will likely yield similar results in those cases. And fortunately for us, there are a lot of these "psychological stops" occurring. The problem we have is when we don't get a psychological stop. If our attacker fights through the pain and continues to victimize us, we might want a round that causes the most damage possible. In essence, we are relying on a "physical stop" rather than a "psychological" one. In order to physically force someone to stop their violent actions we need to either hit him in the Central Nervous System (brain or upper spine) or cause enough bleeding that he becomes unconscious. The more powerful rounds look to be better at doing this....

   • Also see the FBI paper entitled "Handgun Wounding Factors and Effectiveness", by Urey W. Patrick. Agent Patrick, for example, notes on page 8:

     ...Psychological factors are probably the most important relative to achieving rapid incapacitation from a gunshot wound to the torso. Awareness of the injury..., fear of injury, fear of death, blood or pain; intimidation by the weapon or the act of being shot; or the simple desire to quit can all lead to rapid incapacitation even from minor wounds. However, psychological factors are also the primary cause of incapacitation failures.
     
     The individual may be unaware of the wound and thus have no stimuli to force a reaction. Strong will, survival instinct, or sheer emotion such as rage or hate can keep a grievously wounded individual fighting....

   
   
4. And for some more insight into wound physiology and "stopping power":
   
   
   • Dr. V. J. M. DiMaio (DiMaio, V. J. M., M. D., Gunshot Wounds, Elsevier Science Publishing Company, 1987, pg. 42, as quoted in In Defense of Self and Others..., Patrick, Urey W. and Hall, John C., Carolina Academic Press, 2010, pg. 83):

     In the case of low velocity missles, e. g., pistol bullets, the bullet produces a direct path of destruction with very little lateral extension within the surrounding tissue. Only a small temporary cavity is produced. To cause significant injuries to a structure, a pistol bullet must strike that structure directly. The amount of kinetic energy lost in the tissue by a pistol bullet is insufficient to cause the remote injuries produced by a high-velocity rifle bullet.

   • And further in In Defense of Self and Others... (pp. 83-84, emphasis in original):

     The tissue disruption caused by a handgun bullet is limited to two mechanisms. The first or crush mechanism is the hole that the bullet makes passing through the tissue. The second or stretch mechanism is the temporary wound cavity formed by the tissue being driven outward in a radial direction away from the path of the bullet. Of the two, the crush mechanism is the only handgun wounding mechanism that damages tissue. To cause significant injuries to a structure within the body using a handgun, the bullet must penetrate the structure.

   • And further in In Defense of Self and Others... (pp. 95-96, emphasis in original):

     Kinetic energy does not wound. Temporary cavity does not wound. The much-discussed "shock" of bullet impact is a fable....The critical element in wounding effectiveness is penetration. The bullet must pass through the large blood-bearing organs and be of sufficient diameter to promote rapid bleeding....Given durable and reliable penetration, the only way to increase bullet effectiveness is to increase the severity of the wound by increasing the size of the hole made by the bullet....

   
   
5. Urey Patrick was in the FBI for some 24 years, 12 of which were in the firearms training unit where he rose to the position of Assistant Unit Chief. John Hall is an attorney who spent 32 years in the FBI, including serving as a firearms instructor and a SWAT team member.
   
   
6. And sometimes a .357 Magnum doesn't work all that well. LAPD Officer Stacy Lim who was shot in the chest with a .357 Magnum and still ran down her attacker, returned fire, killed him, survived, and ultimately was able to return to duty. She was off duty and heading home after a softball game and a brief stop at the station to check her work assignment. According to the article I linked to:

   ... The bullet ravaged her upper body when it nicked the lower portion of her heart, damaged her liver, destroyed her spleen, and exited through the center of her back, still with enough energy to penetrate her vehicle door, where it was later found....