Indirect ballistic injuries

[Michael Courtney]

"Energy transfer" is really NOT a significant factor. Why? Because if the bullet is breaking apart, that energy is being transferred to the destruction of the bullet, not to the target. Same with expansion.

Only a small fraction (< 10% in most cases) of the bullet's kinetic energy is absorbed by expansion and/or fragmentation of the bullet.

The retarding force between bullet and tissue is exactly equal to the local rate of the projectile's kinetic energy loss. This is the force that is responsible for indirect tissue injuries incapacitating effects.

A bullet that loses 40% of its mass to fragmentation will have a peak retarding force roughly 40% larger than a comparable bullet (same impact energy and penetration depth) that does not fragment. This significant increase in retarding force is much larger than the relatively insignificant differences in energy required to deform/fragment the bullets.

What is important is the wound channel. how big it is and what it destroys.

No one debates whether or not the wound channel is important. The question is whether or not the wound channel is the only thing that is important. There is a growing body of scientific evidence that provides compelling support for the idea that distant effects also play an important role.

It isn't the "transfer of energy" that creates tissue destruction.

The Textbook of Military Medicine cites plenty of research documenting the importance of local transfer of energy in tissue destruction. Are you somehow more enlightened by the MDs and PhD's who conducted the original research and the US Military surgeons who reviewed the material and included it in the Textbook of Military Medicine?

Also, flat bullets have greater impact effect than spitzer bullets. So you can get a "splash" from a flat or blunt bullet at less velocity than you could with a pointed bullet.

Expansion turns a spitzer bullet into a more blunt projectile. Tumbling in tissue also gives a blunter profile to a spitzer bullet.

I've always heard that with the spitzer type bullets, you need a velocity of 2600 fps to actually get an effective hydraulic reaction. Anything less than that would require a blunter bullet.

The effectiveness of tissue effects needs to be parameterized in terms of the projectile's loss of kinetic energy rather than velocity. There are some excellent graphs that describe this in the Textbook of Military Medicine. Remote effects have been documented for AK47 bullets (< 2600 FPS, spitzer bullets) that apparently did not tumble.

I would estimate that distant effects are likely for bullets that lose more than 100 ft-lbs of energy in an inch of penetration if it occurs sufficiently close to vital organs. There are certainly plenty of documented examples suggesting this criteria is reasonable.

Michael Courtney

 

[JesseL]

The Textbook of Military Medicine cites plenty of research documenting the importance of local transfer of energy in tissue destruction. Are you somehow more enlightened by the MDs and PhD's who conducted the original research and the US Military surgeons who reviewed the material and included it in the Textbook of Military Medicine?

Medical doctors aren't physicists. Don't credit them with too much knowledge and understanding of how bullets actually cause the damage that they have to clean up.

"Energy tranfer" is a lousy term to work with in these debates. If what we were talking about was actually just energy transfer, all a bullet would do is raise the temperature of the flesh a few degrees. There are wounds that involve far less kinetic energy than a bullet and do damage every bit as lethal (broadhead arrows and butcher knives come to mind), and there are wounds where 100% of a bullets energy is tranfered to a body with only superficial injury (such as being hit in a bullet proof vest).

 

[Phil DeGraves]

Expansion turns a spitzer bullet into a more blunt projectile. Tumbling in tissue also gives a blunter profile to a spitzer bullet.

Well, DUH! I'm just saying that you don't need as much velocity to create the same "splash" if you have a wadcutter or similarly shaped bullet. And that bullet, going slower will have much less kinetic energy (and therefore less potential "energy transfer" while still having the same chance of distance effects). A blunt bullet will deposit the energy more quickly than a spitzer. So maybe there are multiple factors at work here (you think?), one being the speed at which the energy is being deposited to the target as opposed to the raw energy potential.

The Textbook of Military Medicine cites plenty of research documenting the importance of local transfer of energy in tissue destruction.

I would agree that the potential for tissue destruction is directly proportional to the kinetic energy of the projectile, but it is awfully difficult to separate the individual components in a manner as to which gets the credit for "tissue destruction." As you have said, the higher the energy, the more likely the bullet is to expand or break apart creating larger or secondary wound channels with accompanying tissue destruction. It isn't the energy transfer per se that is destroying the tissue but how the effects of the energy in other aspects are deposited and to say "It's the energy transfer that did this" would be a stretch. The Glaser Safety Slug is a good example of a 100% "energy transfer" round that if not placed in the correct area of the body, fail to do much at all, not even being able to break bones.

The effectiveness of tissue effects needs to be parameterized in terms of the projectile's loss of kinetic energy rather than velocity.

Yes, assuming that a sufficient kinetic energy is available which is highly dependent on the velocity. But then again, you've left out the important factor of Ballistic coefficient or bullet shape.

I would estimate that distant effects are likely for bullets that lose more than 100 ft-lbs of energy in an inch of penetration if it occurs sufficiently close to vital organs.

Again, this does not take into account bullet shape which can create just as big a splash with much less velocity and kinetic energy
and some organs are less susceptible to stretch and therefore distance effects than others.

 

[brickeyee]

That sounds reasonable, bet remember that the speed of sound in water (and similarly flesh, which is mostly water) is nearly 5000 fps. I'm not aware of any physical threshold encompassed by the spectrum of normal bullet velocities that would have an impact on terminal ballistics.

I was not intending to imply that the speed of sound in flesh would be exceeded, just that at these energy regimes the behavior of material may not be the same as under simple static measurements.

There is going to be a change in tissue behavior when the energy level is high enough to cause tearing instead of simple deformation.
Once the tissue is actual torn its ability to resist further deformation is going to be decreased.

Stretch a rubber band and you will have the same basic behavior until it breaks.

The anisotropy of tissue and the many actual types (with slightly varying densities and elastic behavior) that a projectile can pass through (multiple type in even a simple thorax wound) are complicating factors to the actual effects that result.

Fuel air type weapons do not produce as high a peak pressure as high explosive weapons, but the duration (and resulting impulse) are larger in air-fuel type weapons.
The under pressure that follows a large fuel-air explosion may also contribute to the lethality.

I deal with satellites, and the impact regime for foreign objects is a notch higher than any kinetic behavior on earth.
The energy levels are so high that plasma is produced from both the impacting object and the material it strikes.
The atoms are vaporized and charges separated.
There is no way to predict these kind of changes in how material behaves from static measurement a priori.
We can understand what is happening after the fact, and even predict what will happen now that we have some knowledge, but the behavior was strange when initially observed.

 

[Michael Courtney]

That sounds reasonable, bet remember that the speed of sound in water (and similarly flesh, which is mostly water) is nearly 5000 fps. I'm not aware of any physical threshold encompassed by the spectrum of normal bullet velocities that would have an impact on terminal ballistics.

One of many myths in wound ballistics is the idea that normal bullets cannot exceed the speed of sound in tissue. As pointed out in the Textbook of Military Medicine, The speed of sound in the lungs is roughly 50 m/s.

Michael Courtney

 

[Michael Courtney]

Medical doctors aren't physicists. Don't credit them with too much knowledge and understanding of how bullets actually cause the damage that they have to clean up.

Actually, Bo Janzon, who wrote a number of important papers supporting the importance of energy transfer, has a master's degree in Engineering Physics and a PhD in Medical Science. His work is highly esteemed in the field of wound ballistics, and much of it is incorporated into the Textbook of Military Medicine.

"Energy tranfer" is a lousy term to work with in these debates. If what we were talking about was actually just energy transfer, all a bullet would do is raise the temperature of the flesh a few degrees.

Energy is transferred to tissue in a number of forms, the least of which is heat. In the chapter, "The Physics and Biophysics of Wound Ballistics," The Textbook of Military Medicine describes these different forms and their relative importance in damaging tissue. This chapter is mandatory reading for folks who aspire to discuss wound ballistics intelligently.

There are wounds that involve far less kinetic energy than a bullet and do damage every bit as lethal (broadhead arrows and butcher knives come to mind),

These kinds of wounds involve only direct tissue injuries. Low-energy wounds are dominanted by direct injury mechanisms. Indirect injuries come into play at the higher energy levels.

and there are wounds where 100% of a bullets energy is tranfered to a body with only superficial injury (such as being hit in a bullet proof vest).

When body armor stops a bullet, most of the energy is absorbed by the armor; only a small percentage is transferred to the body. The percentage of a bullet's energy that is transferred to the body when stopped by body armor depends on the armor's backface deformation, which can be measured as the impression made in a plasticine backing behind the armor in laboratory tests. The NIJ standard allows a maximum backface deformation of 44mm.

Behind-armor trauma is a field of active research in wound ballistics. When armor stops a bullet with close to 44mm of deformation, less than 25% of the energy is transferred to the target (the rest is absorbed by the armor). Armor with less deformation absorbs even more of the energy. Armor with 25mm of deformation transmits less than 10% of the impact energy to underlying tissue.

Studies in human-sized pigs have shown that transmitting handgun levels of kinetic energy to underlying tissue can produce serious injuries, rapidly depressed EEG readings, and even death in a significant percentage of hits.

Michael Courtney

 

[Phil DeGraves]

I would estimate that distant effects are likely for bullets that lose more than 100 ft-lbs of energy in an inch of penetration if it occurs sufficiently close to vital organs.

So a .32 S&W that gets stopped by the breastbone (100% energy transfer, 100 lbs of energy within an inch of penetration and close to vital organs) is going to create distance effects on those organs? I doubt it.

 

[Michael Courtney]

So a .32 S&W that gets stopped by the breastbone (100% energy transfer, 100 lbs of energy within an inch of penetration and close to vital organs) is going to create distance effects on those organs? I doubt it.

How many bullets with 100 ft-lbs of energy get stopped by direct hits to the breastbone that have not already lost a lot of energy passing through intermediate barriers or thick clothing? I bet you can't cite any published examples to support your myth of the breastbone's stopping power. Auto glass, doors, furniture, a thick heavy coat or even a leather jacket can easily rob 50ft-lbs from a penetrating bullet. Of course, this greatly reduces the impact forces and potential for distant wounding.

In addition, a bullet losing 100 ft-lbs in 1" exerts a force of 1200 lbs. Even though the heart seems to be the thoracic organ most resistant to distant effects, there are plenty of examples of cartiac arrest and arrythmia resulting from impact of similar force to the chest, although the more likely results are internal contusions which are not life threatening.

There are plenty of examples of low-energy bullets being stopped by bone while creating significant injuries to tissue beyond the bone.

Michael Courtney

 

[walking arsenal]

Medical doctors aren't physicists.

And physicists aren't medical doctors. That argument could go either way.

Someone mentioned earlier about about a spike in blood pressure from trauma causing injury to the brain. I'd like to hear more about that.

 

[Michael Courtney]

The retarding force between bullet and tissue is the key parameter when understanding the potential for distant injuries. The attached figure shows a plot of retarding force vs. penetration for a 30 caliber bullet in ballistic gelatin. (This figure is Fig 4-9 in the Textbook of Military Medicine converted to english units.) The sudden increase at 6" of penetration is the result of bullet yaw. Prior to yaw, the bullet actually has a smaller retarding force than many service caliber handgun JHPs.

It has been documented that these levels of retarding force can produce remote injuries:


The following example from the WDMET database may be an example of just such an injury: A soldier sustained a through-and-through of the shoulder made by an AK47 bullet fired from about 50 m away (Figure 4-39). A roentgenogram made about 1 hour after wounding (Figure 4-40) shows that the lung nearest the wound has an extensive pulmonary contusion. The cause of this injury is not clear. If temporary cavitation were the cause, some evidence of chest-wall damage or even a fracture of the humerus might be found. Certainly, the soft-tissue injury shows no evidence (such as ecchymosis) of the effects of massive temporary cavitation that would be necessary to have caused this distant lung injury. Could this observed injury be a manifestation of stress waves?


See: pp 121, 146-149 in

Bellamy RF, Zajtchuk R. The physics and biophysics of wound ballistics. In: Zajtchuk R, ed. Textbook of Military Medicine, Part I: Warfare, Weaponry, and the Casualty, Vol. 5, Conventional Warfare: Ballistic, Blast, and Burn Injuries. Washington, DC: Office of the Surgeon General, Department of the Army, United States of America; 1990: 107-162.

Downloadable from:

http://www.bordeninstitute.army.mil/published_volumes/conventional_warfare/conventional_warfare.html

For comparison, the peak retarding force of a 5.56mm FMJ bullet is roughly 2500 lbs at yaw. A number of service caliber JHP handgun loads produce comparable (> 2000 lbs) peak retarding forces.

Michael Courtney