Temporary Cavitation Re-Visited (DocGKR?)

[Terminal Effect]

My question regarding temporary cavitation of FMJ/OTM rifle projectiles is the following:
does it occur that the mechanical forces (stretch) of a penetrating projectile cause tissue damage to structures except the liver and brain/CNS? I would assume that this is quite rare...

From the reading I have done the projectile will cause maximum displacement of tissue when it is at 90°. This leads to my second question: How far can muscle tissue (e.g. thigh wound) be stretched without disruption?

Third question: would it be physically possible to design a land-warfare-legal rifle bullet which actually utilizes its stretch potential to do damage on someone; i.e. criminal/terrorist, given I am referring to elastic tissues?

Lastly, am I right in the assumption that only soft-point bullets have the ability to cause massive and extensive "shock waves" that can disrupt even elastic tissues such as muscle/organs?
IIRC, Dr. Fackler wasn't quite sure if blunt trauma (right terminology?) could cause spinal paralysis while hunting or in perpetrators.
Alas, from the medical literature of various articles by Dr. Fackler et al. I have noticed that temporary cavitation is largely to be disregarded as a wounding mechanism. Agent Urey also emphasized this.

Nevertheless, I wanted to start a discussion on the issue to learn some more.
Plus, I especially wanted to evoke an answer from the [i]real experts[i] (Dr.Roberts)

I appreciate any knowledgeable input. Thank you for your time.
-David

PS I have used the search function for M4 and TF...

[Terminal Effect]

from TF by desert101: this is part of an ongoing old discussion there.

The reference to "one side fixed" refers to the common anatomic feature of organ fixation at one point of the structure, while the other areas of the organ are allowed to "float or move". Examples would include the liver, which is attached by several fascial like ligaments b but the liver moves to a degree on these attachments. The trauma relevance in blunt trauma: sudden deceleration pulls on the fascial attachments, as well as the large blood vessel attachments. If the deceleration forces are sufficient, the blood vessel attachments and even the ligamentous attachments can fail, the liver tearing from its harness with obvious poor outcomes.

Similarly, other organs tend to suffer from excessive forces which are focused at the points of attachment.

With regards to temporary cavity, part of the relevant discussion (in inelastic organs) would be physiologic dysfunction, as opposed to histologic destruction, which is seen on pathologic examinations. Physiologic dysfunction is, of course, much more difficult to track and prove.

[bernieb90]

Originally Posted by Terminal Effect

My question regarding temporary cavitation of FMJ/OTM rifle projectiles is the following:
does it occur that the mechanical forces (stretch) of a penetrating projectile cause tissue damage to structures except the liver and brain/CNS? I would assume that this is quite rare...

From the reading I have done the projectile will cause maximum displacement of tissue when it is at 90°. This leads to my second question: How far can muscle tissue (e.g. thigh wound) be stretched without disruption?

In general there are 2 very distinct behaviors that we observe with regards to FMJ/OTM type rifle projectiles.

The first is exactly as you describe. Penteration through soft tissue followed by yaw with no bullet fragmentation. This is typical of what we would see with 7.62 caliber M80 ball (except West German Steel jacketed), as well as .223 Wolf FMJ, and other thick jacketed FMJ type rifle bullets. In this case it is not uncommon for the elastic tissue of the body to easily deal with the size of the temporary cavity generated, with little additional damage. There are a few exceptions to this. If the max temprary cavity occurs near the exit (the bullet is yawing as it exits) then the exit wound will be much larger than if the bullet exited point forward. And as you mentioned if non-elastic organs are penetrated such as the brain, liver, or spleen then increased trauma will occur.

The second type of behavior we see with FMJ/OTM type projectiles is penetration followed by yaw, and fragmentation. This fragmentation is highly velocity dependent, and bullets below fragmentation velocity will behave like the example above. Fragmentation is most typically seen in high velocity .223/5.56 projectiles such as those use in M193, M855, MK262, as well as 68/75gr OTMs from hornady, and 69/77gr OTMs from Sierra.

Dr Roberts describes the synergystic effect of temporary cavity combined with fragmentation as follows:

Rifle Bullet Fragmentation Mechanism
1. The rifle bullet fragments in tissue.
2. Multiple fragments spread out radially from the wound tract.
3. Temporary Cavitation stretches tissue.
4. The multiply perforated tissue cannot absorb the stretch which would ordinarily be tolerated by intact tissue.
5. The weakened tissue is torn and disrupted.

Originally Posted by Terminal Effect

Third question: would it be physically possible to design a land-warfare-legal rifle bullet which actually utilizes its stretch potential to do damage on someone; i.e. criminal/terrorist, given I am referring to elastic tissues?

That is exactly what yawing fragmenting bullets do.

Originally Posted by Terminal Effect

Lastly, am I right in the assumption that only soft-point bullets have the ability to cause massive and extensive "shock waves" that can disrupt even elastic tissues such as muscle/organs?
IIRC, Dr. Fackler wasn't quite sure if blunt trauma (right terminology?) could cause spinal paralysis while hunting or in perpetrators.
Alas, from the medical literature of various articles by Dr. Fackler et al. I have noticed that temporary cavitation is largely to be disregarded as a wounding mechanism. Agent Urey also emphasized this.

You would be incorrect in that assertion. Yawing/fragmenting bullets cause very large temporary cavities with subsequent tissue destruction. Soft point bullets in .223/5.56 tend to cause significantly less damage that fragmenting OTMs. Larger calibers such as .308 can utilize far more effective bullets such as 155gr A-max while maintaining 12" minimum penetration.

[Terminal Effect]

Bernieb90 thank you very much. Did you by chance get my previous PMs?

[Terminal Effect]

To summarize we could say then, that: a yawing bullet which causes a large temporary cavity is a lot less effective in terms of wounding mechanism than a bullet which yaws and fragments.

From this I could extrapolate: the yaw of the bullet will cause more damage because more tissue is being crushed by the bullet due to the fact that its contact area with the tissues is larger.

Furthermore, as you have stated, temporary cavitation must work in synergy with fragmentation effects to cause lesions.

Hence, the stretch [b]without[b] fragmentation is to be disregarded when we speak of elastic tissues. Is that correct?

However, I have second thoughts due to the following article:

Here's a snip from it : [b]The temporary cavity caused by common handgun bullets
is too small to be a significant wounding factor in all but the
most sensitive tissues (brain and liver) [4]. Center-fire rifle
bullets and large handgun bullets (e.g., .44 magnum) often
induce a large temporary cavity (10-25 cm [4-10 in.] diameter)
in tissue. This can be a significant wounding factor,
depending on the characteristics of the tissue in which it
forms [4, 13].
B
Fig. 3.-A and B, High-speed radiographs of thigh of a cat during (A)
and after (B) passage of a 4/32-in. (3.2 mm) steel sphere with impact
velocity of 3200 ft/sec (975 rn/see). Sciatic nerve of cat’s thigh made
radiopaque with iodobenzene. Images obtained with beam parallel to path
of missile.
Microsecond radiograph during passage (A) shows anterior displacement
of sciatic nerve by temporary cavity. Tissues surrounding path of
projectile are undergoing blunt trauma and tissue stretch because of
temporary cavity formation.
Radiograph made Immediately after shot (B) shows permanent cavity
(wound channel) is considerably smaller than temporary cavity. Sciatic
nerve is in its usual anatomic position. Nerve and vessel injury from stretch
may have occurred. (Courtesy of Leonard D. Heaton, James B. Coates, Jr.,
and James C. Beyer; reprinted with permission from Wound Ballistics,
Office of the Surgeon General, Department of the Army, 1962, p. 209.)
688 HOLLERMAN ET AL. AJR:155, October 1990
ı
.;
Near-water-density, less elastic tissue (e.g., brain, liver, or
spleen), fluid-filled organs (including the heart, bladder, or
gastrointestinal tract), and dense tissue (e.g., bone) may be
damaged severely when a large temporary cavity contacts
them [1 1 ]. More elastic tissue (e.g., skeletal muscle) and
lower-density elastic tissue (e.g., lung) are less affected by
the formation of a temporary cavity [1 4, 15]. Because of these
tissue differences, the transmitted forces of temporary cavitation
caused by a bullet traveling 800-950 m/sec can cause
a more severe pulmonary contusion when the bullet traverses
the chest wall musculature than the pulmonary contusion that
would have occurred had the same bullet passed directly
through the lung [3, 15, 16].
Although formation of a large temporary cavity often has
devastating effects in the brain or liver, its effect in wounds
of the extremities has frequently been exaggerated in articles
about wound ballistics [4, 6, 17]. Fracture of large bones not
hit by the bullet and tearing of major vessels or nerves by the
temporary cavity are often mentioned in the literature (e.g.,
DeMuth [3]), but are rare in clinical experience. This includes
a systematic review of 1400 rifle wounds sustained in the
Vietnamese War and analyzed in the Wound Data and Munitions
Effectiveness Team (WDMET) study (Bellamy RF, personal
communication). Most of the permanent damage in
wounds of the extremities is the result of structures being hit
by the intact bullet, bullet fragments, or secondary missiles.
As in all blunt trauma, shear forces develop and tear structures
at points where one side is fixed and the other side is
free to move. The temporary cavity is no exception. In the
unlikely event that the blunt trauma of the temporary cavity
tears a vessel wall, this is particularly likely to occur at the
vessel origin.
Ballistic Properties and the Wound Produced
Recent controlled animal experiments with military

from ajronline.org

[bernieb90]

Originally Posted by Terminal Effect

To summarize we could say then, that: a yawing bullet which causes a large temporary cavity is a lot less effective in terms of wounding mechanism than a bullet which yaws and fragments.

From this I could extrapolate: the yaw of the bullet will cause more damage because more tissue is being crushed by the bullet due to the fact that its contact area with the tissues is larger.

Furthermore, as you have stated, temporary cavitation must work in synergy with fragmentation effects to cause lesions.

Hence, the stretch [b]without[b] fragmentation is to be disregarded when we speak of elastic tissues. Is that correct?

Disregarded may be too strong a word. A better description may be unreliable. There MAY be additional wound trauma caused even to some elastic tissue under some circumstances given a large enough temporary cavity (such as those created by yawing, but not fragmenting rifle bullets). However those mechanisms will tend to be variabe when dealing with elastic tissue. A yawing FMJ becomes far more effective if bone is struck as this creates secondary projectiles, and may cause the bullet to break up.

FWIW I have seen the effect on game of both the Winchester Failsafe, and Barnes X bullet fired from .308/30-06. Both shots resulted in instant stops of 100lb hogs despite a lack of fragmentation. The 150gr Failsafe fired from the .308 broke the leg bone cut the aorta, and then broke the off side leg when it exited. The animal expired within seconds. In general FMJs that exhibit early yaw, and solid copper bullets can be very effective despite a lack of fragmentation. This is especially true on larger game where penetration if often more desirable than fragmentation or large expansion. The ability to break bones and penetrate to the vitals becomes critical in some situations. The requirements for tactical loads for use in urban areas are different in the the typical target is smaller (12" of penetration is enough), and overpentration is a liability (not the case when hunting or shooting at large concentrations of enemy forces). Specialized use of barrier loads is the exception where again penetration, and expansion must be balanced to allow incapacitation of a target behind the barrier. These loads are typically similar to those used on large game.

[Terminal Effect]

Excellent info, Bernieb90. Thank you.
I respect your knowledge of hunting and tactical applications relevant to my question. However, I am wondering, would it be possible if Dr Roberts could add anything to this?
Just to get the expert's view...

[Glock17JHP]

OK... a little humor is in order...

Sorry, I can't resist... no offense, OK?

That avatar picture looks like a woman's torso...

[Terminal Effect]

That was a good one! Usually I constantly have those things on my mind. In this case, as an exception to the rule, I did not see it.

I don't know if you guys realise it, but it is actually ballistic gelatin being photographed at the time of impact.

By the way, would it by any chance be possible to get Dr. Roberts to add anything to this post?

I know he's not known for his humour(maybe in real life he is), but we all know and respect his immense knowledge and experience in the field of terminal ballistics.

I have been constantly mulling over the issue of temporary cavitation and would like to close that learning chapter and move on... but without final words/corrections from an expert (i.e. Dr. Roberts) I am unable to let it go.

Dave.

[Glock17JHP]

Yes... it is obvious that it is ballistic gelatin...

[Glock17JHP]

Originally Posted by Terminal Effect

I have been constantly mulling over the issue of temporary cavitation and would like to close that learning chapter and move on... but without final words/corrections from an expert (i.e. Dr. Roberts) I am unable to let it go.

Dave.

I would just let it go and keep perusing the information that is already here...

[DocGKR]

"To summarize we could say then, that: a yawing bullet which causes a large temporary cavity is a lot less effective in terms of wounding mechanism than a bullet which yaws and fragments."

Depends on the tissue type and size of temporary stretch.

"From this I could extrapolate: the yaw of the bullet will cause more damage because more tissue is being crushed by the bullet due to the fact that its contact area with the tissues is larger."

Yes; in addition, at max yaw, temporary stretch is generally maximized.

"Furthermore, as you have stated, temporary cavitation must work in synergy with fragmentation effects to cause lesions."

No! Temporary stretch can be quite effective at damaging inelastic tissues, as well as elastic tissue when their maximum stretch threshold is exceeded.

"Hence, the stretch without fragmentation is to be disregarded when we speak of elastic tissues. Is that correct?"

No. See above.

[Terminal Effect]

Thank you thank you thank you, Dr. Roberts.

[Pasteur]

I've always considered that studies of bullets stopped by armor could provide valuable information on ballistic wounding potential other than the tissue directly crushed by the bullet. The region of stretch and hemorrhaging induced in cases where the armor stops a bullet is usually much smaller than an unobstructed bullet that penetrates, but recent research in this field (called behind armor blunt trauma, BABT) have made some relevant observations.

The Swedish Defense Forces, for example, have documented rapid EEG suppression (which they infer could cause unconsciuosness), apnea (cessation of breathing), significant lung injury, and even death in studies on pigs where the bullet was stopped by armor over the lungs. Several physical mechanisms have been suggested for the rapid EEG suppression and apnea including energy transmission to the brain by means of a pressure wave, a vaso-vagal reflex, reduced oxygen uptake, and vasodilation.

A lot has been published in this field, and groups at Johns Hopkins and Wayne State University also have active research programs in BABT. BABT studies are beginning to answer the question of why trauma is not always localized at the impact site, as one might expect. Stress waves are produced by the impact and can create remote damage by means of focussing effects. It is even possible for true shock waves to be produced in the lungs because the speed of sound in the lungs is so small that it can be exceeded by the speed of the chest wall responding to impact. The forces and accelerations involved when a bullet is stopped by armor are tremendous and can create a much different injuries than lower speed impacts associated with sports and vehicles.

[Molon]

Originally Posted by Pasteur

I've always considered that studies of bullets stopped by armor could provide valuable information on ballistic wounding potential other than the tissue directly crushed by the bullet. The region of stretch and hemorrhaging induced in cases where the armor stops a bullet is usually much smaller than an unobstructed bullet that penetrates, but recent research in this field (called behind armor blunt trauma, BABT) have made some relevant observations.

The Swedish Defense Forces, for example, have documented rapid EEG suppression (which they infer could cause unconsciuosness), apnea (cessation of breathing), significant lung injury, and even death in studies on pigs where the bullet was stopped by armor over the lungs. Several physical mechanisms have been suggested for the rapid EEG suppression and apnea including energy transmission to the brain by means of a pressure wave, a vaso-vagal reflex, reduced oxygen uptake, and vasodilation.

A lot has been published in this field, and groups at Johns Hopkins and Wayne State University also have active research programs in BABT. BABT studies are beginning to answer the question of why trauma is not always localized at the impact site, as one might expect. Stress waves are produced by the impact and can create remote damage by means of focussing effects. It is even possible for true shock waves to be produced in the lungs because the speed of sound in the lungs is so small that it can be exceeded by the speed of the chest wall responding to impact. The forces and accelerations involved when a bullet is stopped by armor are tremendous and can create a much different injuries than lower speed impacts associated with sports and vehicles.

I don't suppose you have any factual data to support such claims?

[Pasteur]

Originally Posted by Molon

I don't suppose you have any factual data to support such claims?

Why do you doubt?

The assertions above are well supported by publications from such luminaries in biomechanics as YC Fung and shock wave physics as Brad Sturtevant, as well as by publications in top tier scientific journals including the Journal of Trauma, Military Medicine, and Journal of Biomechanics, and Journal of the Royal Army Medical Corps. One example of many:

Biophysics of impact injury to the chest and abdomen
Authors: G J Cooper, D E Taylor
The physical mechanism of blunt impact injuries to thoracic and abdominal viscera is often conveniently described simply in terms of "crush"--this is an over-simplification. Any impact to the torso does result in the rapid displacement of the body wall which may lacerate and contuse underlying viscera, but this simple explanation does not account for pathology at sites some distance from the contact point and does not adequately describe the dependence of the severity and location of injury upon the rate of energy transfer. Quite minor displacements of the body wall may produce serious injury if the body wall velocity is high. The motion of the body wall generates waves that propagate within the body and transfer energy to internal sites. The nature and properties of these waves are discussed in simple terms and the role of waves in the production of the characteristic injuries resulting from impact to the torso is presented.
Journal of the Royal Army Medical Corps.1989/06;135(2):58-67.

A second example:

Shock waves are high-pressure waves characterized by an effectively instantaneous wavefront propagated through the underlying tissue at a velocity faster than the speed of sound in tissue. A shock wave can be considered a special form of a stress wave. Stress waves in tissue may result in very high local forces, producing small but very rapid distortions of tissue (strain). When lightweight projectiles having the capacity for nonpenetrating impact injury are traveling at high speeds, the high initial wall velocities tend to excite the high-frequency compression waves to produce direct and indirect trauma. Shear waves may produce marked distortion of internal organs. The distortion in organs adjacent to the body wall may produce local shear, resulting in contusion or laceration. Crush injury can result in hollow viscous perforation by a sudden rise in intraluminal pressure. J Trauma. 2005;58:1241–1251.

A google scholar search for "Behind Armor Blunt Trauma" will reveal many more.

To my knowledge, these BABT results are widely accepted in the scientific community, and no contrary data has been published. Are you aware of any contrary data from scientific sources?

[Glock17JHP]

Deja Vu... I feel like I'm back on 'GlockTalk'!!!

[ToddG]

I don't know any serious educated person who will tell you the book is closed on terminal ballistics. Everyone appreciates that current science and ethical testing protocols allow us to go only so far.

We know that traditional wounding (pen/exp, non-temporary tissue damage) plays a major, demonstrable, predictable role.

We also know that people sometimes, perhaps often, cease to be violent or even conscious when those traditional wounding mechanisms, alone, would not be seen as the sole cause. It is vogue to refer to every such instance as a "psychological stop" but the reality is that we cannot prove the mechanism(s) involved. Are some of them psychological in nature? Absolutely. Are all of them? No one can say.

There's a major leap between saying "we know pen/exp works" and "we know that only pen/exp works."

[Terminal Effect]

Pasteur- your theory sounds educated, so I will choose my words carefully .

But, IIRC, in the DVD "Deadly Effects" Dr. Jason is shot in the torso whilst wearing body armor. He is neither knocked down, nor is he physically affected by shock waves behind his vest...


Again, this is discussed on:


www.firearmstactical.com

I don't have time to find the exact link.



Quote:
"Furthermore, as you have stated, temporary cavitation must work in synergy with fragmentation effects to cause lesions."
No! Temporary stretch can be quite effective at damaging inelastic tissues, as well as elastic tissue when their maximum stretch threshold is exceeded.
Here's my question: scenario: elastic tissue under stress through TC/shock waves. You mentioned the maximum stretch threshhold. Could you estimate as of when this is reached in centimeters? 15, 20 , more?
Quote:
"Hence, the stretch without fragmentation is to be disregarded when we speak of elastic tissues. Is that correct?"
No. See above.
Last edited by DocGKR; 04-05-2009 at 06:18 PM.

[Pasteur]

Originally Posted by Terminal Effect

Pasteur- your theory sounds educated, so I will choose my words carefully .

But, IIRC, in the DVD "Deadly Effects" Dr. Jason is shot in the torso whilst wearing body armor. He is neither knocked down, nor is he physically affected by shock waves behind his vest...


Again, this is discussed on:


www.firearmstactical.com

I don't have time to find the exact link.

Just as every penetrating projectile will not produce certain effects, neither will every projectile stopped by armor. BABT is an active research field, and the scientific community is in the process of quantifying causes and effects. Scientists have suggested that important physical quantities are peak chest wall force, acceleration, and velocity. Data shows that BABT is likely for forces above 10,000 newtons, accelerations above 1000 g's, and peak chest wall velocities above 10 m/s (at ballistic strain rates). Since obtaining these quantities requires carefully designed experiments and/or complex numerical modeling (FEM), researchers have also made progress expressing the risk of BABT in terms of more easily determined impact energy and armor backface deformation. Backface deformation is determined by measuring the indent in clay backing (armor over clay) according to a procedure specified by the NIJ.

The NIJ standard specifies a maximum backface deformation of 44mm. However, the original animal experiments on which this was based focussed on projectiles up to only 400J of impact energy. Subsequent research has shown that as the impact energy is increased, the maximum backface deformation must be decreased (with a better armor design) to keep the risk fo BABT at the same level. Most recent research suggests that any scientific determination of BABT risk requires knowning (at a minimum) the impact energy, the impact location, and the backface deformation measured with the given projectile, impact velocity, and armor. The thickness of the body wall and distance from the armor to the body wall at impact are probably also important.

Researchers in this field have made some attempts to analyze human shooting events, but have been hindered by difficulties in obtaining the necessary data for anything approaching a significant sample size. In addition to needing the relevant ballistic information, significant information about the effects in target are also desirable including X-rays, CT scans, MRI, EEG, ECG, arterial oxygen saturation, heart rate, mean arterial pressure, etc. to determine the physiological effects of possible BABT. Because it is difficult to obtain sufficient information in human shootings, carefully controlled experiments have been conducted in live animal models, where most of the above are available, along with necropsy results.

Several of these live animal experiments have shown that human-sized pigs experience significant wounding and physiological effects (including death) due to BABT. Effects include apnea (non-breathing periods), EEG suppression, decreased oxygen saturation and blood pressure, and severe lung contusions. At lower levels of backface deformation (28mm), experiments show that some of the physiological effects (EEG supression, apnea, blood pressure drop) are reduced by vagotomy (disconnecting the vagus nerve). This is consistent with several other experiments suggesting that physiological responses to chest trauma at high strain rates depends on a vagally mediated response, at least in part.