The myth of the temporary wound cavity

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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. Temporary cavity has no reliable wounding effect in elastic body tissues (emphasis added). Temporary cavitation is nothing more than a stretch of the tissues, generally no larger than 10 times the bullet diameter (in handgun calibers), and elastic tissues sustain little, if any, residual damage.

That’s from the FBI’s study of wound ballistics; and is something that everyone should bear in mind. Temporary stretch cavity is only a significant wounding mechanism in projectiles over 2000 FPS, which no handgun round is going to be able to reach. Why does this matter? Because the discussion of terminal ballistics is fraught with so much myth and nonsense that it’s very easy to lose sight of what a pistol bullet is actually doing. Remember: kinetic energy doesn’t kill, energy dump doesn’t kill, and temporary stretch cavity doesn’t kill. The only wound mechanic of a pistol bullet is the permanent crush cavity, which is the actual path of tissue destroyed by the bullet. For the crush cavity to be significant, it must damage the central nervous system, or cause sufficient blood loss to shut down the body.

Don’t believe the nonsense.

19 thoughts on “The myth of the temporary wound cavity”

  1. Come on… there has to be someone out there carrying a .460 S&W magnum as a defensive weapon. Just like there are derp Kommandos carrying Walther P22’s OC style in an Uncle Mikes contraption.

    Spot on as usual, gel tests do not mean much nor do cavities. I care about penetration in the Goldilocks zone, not too much and not too little. I second the sentiment that if something needs shooting and you have a choice, pick a shotgun/rifle.

    1. “gel tests do not mean much nor do cavities.”

      Um you determine penetration using gel tests, and permanent wound cavity is also a cavity.

  2. “A witch! Burn (him), burn (him)!”

    On a completely unrelated note to the article, I do think it’s time to watch Monty Python and the Holy Grail again…

    “What do you burn apart from witches?”
    “More witches!”

  3. This study does not address rifles vs handguns and mild TBI is not fatal. However, If you want to see what new science has to say about this topic read medical journals and not gun blogs. Generally only abstracts are free unless you belong to a medical library.

    Look at this. (Courtney A and Courtney M have another similar study.)
    http://www.ncbi.nlm.nih.gov/pubmed/18829180

    A thoracic mechanism of mild traumatic brain injury due to blast pressure waves.
    Courtney AC1, Courtney MW.
    Author information
    Abstract
    The mechanisms by which blast pressure waves cause mild-to-moderate traumatic brain injury (mTBI) are an open question. Possibilities include acceleration of the head, direct passage of the blast wave via the cranium, and propagation of the blast wave to the brain via a thoracic mechanism. The hypothesis that the blast pressure wave reaches the brain via a thoracic mechanism is considered in light of ballistic and blast pressure wave research. Ballistic pressure waves, caused by penetrating ballistic projectiles or ballistic impacts to body armor, can only reach the brain via an internal mechanism and have been shown to cause cerebral effects. Similar effects have been documented when a blast pressure wave has been applied to the whole body or focused on the thorax in animal models. While vagotomy reduces apnea and bradycardia due to ballistic or blast pressure waves, it does not eliminate neural damage in the brain, suggesting that the pressure wave directly affects the brain cells via a thoracic mechanism. An experiment is proposed which isolates the thoracic mechanism from cranial mechanisms of mTBI due to blast wave exposure. Results have implications for evaluating risk of mTBI due to blast exposure and for developing effective protection.

    1. We are very specifically only talking about handgun wound ballistics to the thoracic cavity.

      If you want to talk about rifles and headshots, this isn’t the place for it.

      1. The abstract isn’t talking about head shots, it is talking about the potential for TBI due to the pressure wave of a ballistic impact to the thoracic (chest) area. That being said, since they study was done for the US Miilitary Academy – I would guess the primary focus is rifle rounds.

        I would find it hard to believe that ANY handgun round would cause enough of a pressure wave to cause even mild TBI.

        1. I know, I was just trying to fend off any attempt to introduce head shots into the discussion as well. I’ve also seen that abstract before, and IIRC it was more focused on rifle rounds and explosions than handgun rounds.

          1. You mean people would jump in and say you’re wrong without even reading what you wrote?!?!? I’m shocked and disappointed!

  4. You see were its hard to take a 25 year old study as the final word? I’m not saying they are wrong, but the FBI was using 9mm subsonic ammo back then. Not only has bullet technology improved, but medical diagnostics. I’d just like to see something current. I still think shot placement and penetration are more important than anything else, but I can’t help, but wonder what modern science would say about today’s ammo?

    1. There’s at least one 2000 FPS pistol round out there in the wild now (Liberty Civil Defense 9mm and .40) so it might be a topic worth revisiting.

      1. Yes, some of the very light SD ammo can reach the 2000 fps mark, however, it will many years before enough usage has been documented to know if the total result is more effective than the accepted norms. With many users returning to the 9mm due to the accepted SD ammo performance, not sure this specialty ammo will be around for the long term. I think as a civilian we would be better off staying with ammo that is in common usage in LE.

  5. So, Elmer Keith was right all along. He wanted big holes, on both sides to let lots of blood leak out. For the kids who don’t know Elmer, Google him.

  6. Civil Defense ammo is rated around 2000fps, and my FN 5.7 is also about that speed. Maybe some testing of these rounds would yield similar results, maybe they would have different outcomes.

  7. Great post Caleb. Most defensive shooting instructors recognize that to stop a threat the shooter must hit a relatively small area in the upper chest area involving the heart, spine, or lungs (or cranial vault if I may). Lung shots will take longer to disable, heart shots much quicker, and spinal shots can be simultaneous. Outside of that you’re pretty much hurting the bad guy and making him bleed. Even supersonic pistol rounds, which do create some temporary stretch cavity, are mostly effective in the path of the bullet. Shot placement is critical!

    However, if you evaluate the gel shots of many modern defensive pistol rounds you can clearly see the expansive temporary wound cavity that forms just after impact as the bullet expands in soft tissue. Though typically much smaller then rifle cavities, it is possible that a very near miss of something vital (say a major artery, lung, spine, etc.) could produce enough of a shock wave to cause injury to that vital part of the body.

    That injury would have to occur within a few inches of impact, as seen in the gelatin. So, a shot into the chest that just misses the heart, may still damage an artery or lung from that wound cavity. However, that same shot that just misses the spine would not be expected to cause damage to the spine because it is past that expansive temporary wound cavity.

    I’m no doctor, but I’ve seen quite a few gunshot wounds, and this theory seems to hold true.

  8. There is a video on youtube somewhere I recently watched where he says that a man who was shot DIDNT die because the bullet stopped just before it would have hit an artery and bled the man out. It was a hollow point, from what I remember. If a FMJ hits what its supposed to hit its going to stop the threat as easily as a HP. Shot placement is always the key to stopping the attacker. Always. I’ll rely on shot placement over the magical HP any day of the week. And my FMJ’s have a better chance of NOT stopping halfway to the organ or artery Im trying to hit.

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