Temporary cavity?

**KlintonP** · 08-04-13, 05:39

This is something that has bothered me for a LONG time. I often see gel tests that show much more impressive results with a 9mm than a 5.56mm. Before anyone says it, yeah, I read EVERY sticky when they were available. In fact I did more research than that. In the end, it looks as if Doc was very hesitant to assign any major wounding or incapacitation role to the temporary cavity. Yes, he said that a TC can rupture the liver or bladder, or other solid or gas/liquid filled organs. But what does this have to do with a potentially incapactitating shot to the upper chest? To me, nothing. I could easily be misinterpreting terminal ballistics but it would appear to me as if, since TC does no significant muscle, heart, or vascular damage, we should all have larger caliber rifles. Please, someone explain this to me. Again, I have read all stickies and more and fully comprehended this, but still do not understand the superiority of an AR15 over a 9mm Glock. Thank you.

**Alaskapopo** · 08-04-13, 07:05

Originally Posted by KlintonP

This is something that has bothered me for a LONG time. I often see gel tests that show much more impressive results with a 9mm than a 5.56mm. Before anyone says it, yeah, I read EVERY sticky when they were available. In fact I did more research than that. In the end, it looks as if Doc was very hesitant to assign any major wounding or incapacitation role to the temporary cavity. Yes, he said that a TC can rupture the liver or bladder, or other solid or gas/liquid filled organs. But what does this have to do with a potentially incapactitating shot to the upper chest? To me, nothing. I could easily be misinterpreting terminal ballistics but it would appear to me as if, since TC does no significant muscle, heart, or vascular damage, we should all have larger caliber rifles. Please, someone explain this to me. Again, I have read all stickies and more and fully comprehended this, but still do not understand the superiority of an AR15 over a 9mm Glock. Thank you.

At rifle velocity yes the temporary cavity does rip tissue beyond its point of elasticity hence why rifle bullets do much more damage than pistols bullets than only damage tissue the bullet itself touches.
Pat

**T2C** · 08-04-13, 10:08

I am not as well versed in internal, external and terminal ballistics as Doc or some others on this website. My experience is with homicide investigations and ammunition testing before soliciting bids for our agency. Opinions on optimum terminal ballistics vary and I am only going to cover the aspect of calculation of muzzle energy to point you in the direction of finding your answer. You have a lot of reading to do in order get there.

There are a lot of factors when determining why a particular projectile creates a larger temporary cavity in ballistic gelatin. Projectile shape and diameter are two of those factors and disruption of the medium the projectile passes through will be affected by these two factors. That may account for why the temporary wound cavity created by some cartridges appears to be greater than other cartridges that have a better stopping record.

If you compare the muzzle energy of a 9mm 124g + P hollow point cartridge and a 55g SP .223 cartridge, you will see a huge difference in available energy for terminal transfer. The figures are assuming there is no intermediate barrier that will diminish projectile energy.

ME(ft-lbs) = 1/2g x MV(fps) x MV (fps) x Mass(lbs)
ME = muzzle energy
MV = muzzle velocity
g = gravity at 32 ft/sec.sec
fps = feet per second

The stated velocity of the 9mm 124g +P cartridge is 1220 fps. I measured the muzzle velocity of a .223 55g SP cartridge using a chronograph and 16" carbine. The velocity of the .223 projectile at the chronograph is 2953 fps, ES/SD = 86/42 fps @ 15 feet from the muzzle. MV = 2980 fps. Using the energy formula to calculate muzzle energy the results are:

9mm ME = 410 ft.lbs
.223 ME = 1090 ft.lbs

If the target is struck at 25 yards:

9mm Terminal Energy = 367 ft.lbs
.223 Terminal Energy = 1010 ft.lbs

The .223 Terminal Energy is 2.75 times the Terminal Energy of the 9mm at 25 yards. If both projectiles remain inside the target, there should be 100% energy transfer. This does not take projectile expansion or permanent wound cavity into consideration. This is strictly energy transfer.

Some would argue that momentum is a better determining factor for stopping power and using this theory the .223 cartridge would still have an edge over the 9mm.

This is strictly a mathematical explanation of why the .223 should be more effective than the 9mm round using the energy formula.

I have not seen anyone shot with this particular 9mm cartridge, so this is strictly math. I can tell you that the .223 SP cartridge performed as expected on human tissue. I do not have the photographs or measurements from the autopsy report. It is strictly my opinion.

**KlintonP** · 08-04-13, 19:40

Originally Posted by Alaskapopo

At rifle velocity yes the temporary cavity does rip tissue beyond its point of elasticity hence why rifle bullets do much more damage than pistols bullets than only damage tissue the bullet itself touches.
Pat

Thanks for the reply, Pat. See, that's where I'm not so certain, though. I understand the concept for sure, that the brute force of a much faster travelling 5.56, say a TBBC, that has expanded SHOULD create a larger wound. BUT none of Fackler's wound illustrations that I saw ever showed a larger wound cavity than the diameter of the bullet, with the exception of the fragmenting M193/M855. That kind of concerns me. And, Doc seemed very hesitant to ever attribute much wounding potential to the TC. Seems to me that he was trying to basically say what I'm concerned about. I have seen no evidence that cardiac, muscular, or vascular tissue is damaged by a TC. That is where I certainly could be wrong. Just haven't seen it.

**KlintonP** · 08-04-13, 20:00

T2C, thanks for the stop by and response. I appreciate it. I definitely get the energy concept. You have an unorthodox formula for energy there, utilizing the force of gravity. Never seen that, I always saw the basic MxV^2. Regardless, very in depth post, but I'm still not up to par here. Perhaps I painted a distorted picture. We all know that handgun bullets rely solely upon their final diameter and penetration numbers to calculate effective wounding capabilities. It would seem as in rifles we throw that out the window and simply assume they will perform better. But why? Yes, a temporary cavity is created depending on a ratio of size and speed. As in, a large slug will create a TC at modest velocities, as will a streamlined FMJ rifle bullet at significant velocity. But what does it actually do to help us? Fackler and Doc both appear quite hesitant to attribute much wounding capability of the TC to muscle, heart, or vascular tissue. So assuming a decent COM shot, would the wound be any larger with a TBBC over an HST? I'm just not seeing hard evidence of TC creating a bigger wound in the thoracic cavity.

**T2C** · 08-04-13, 23:42

I believe that the theory behind creating a larger TC was more about addressing stopping power than permanent wound cavity. On the other side of the coin, a larger permanent wound cavity facilitates greater blood loss in a given period of time. In an urban environment defeating intermediate barriers, such as automobile glass, is an important consideration. The best anti-personnel round may not be the best fighting round when barriers have to be defeated to reach a threat.

Without interviewing someone who was shot or the shooter to determine the effects of a particular cartridge and how quickly someone was incapacitated, I think it is difficult to rely on temporary wound cavity for effectiveness. That may be why Dr. Fackler would not commit to the temporary wound cavity theory.

Science is a good thing, but I make my defensive ammunition selection through the process of elimination. I avoid anything that I know has not worked well and narrow my choices to cartridges that I believe have worked well in local shooting incidents. Cartridges recommended by Doc happen to be on my list of carry choices.

**vicious_cb** · 08-05-13, 03:55

I do believe that TC at rifle velocities can and does produce horrific tissue damage under the right circumstances but the experts like DocGKR are hesitant to say anything about its effectiveness because of the inherent unpredictability of the wounding mechanism.
Some extreme examples can be seen here:

M193 to the leg

https://www.m4carbine.net/showthread.php?t=31666

vs

9mm Ranger 127 +P+ to the arm

https://www.m4carbine.net/showthread...=129949&page=4

I know these are a small example of the capability of each round and probably extreme examples at that, but it does illustrate the difference in damage a rifle round vs a pistol round can potentially cause.

**KlintonP** · 08-05-13, 08:41

Originally Posted by vicious_cb

I do believe that TC at rifle velocities can and does produce horrific tissue damage under the right circumstances but the experts like DocGKR are hesitant to say anything about its effectiveness because of the inherent unpredictability of the wounding mechanism.
Some extreme examples can be seen here:

I know these are a small example of the capability of each round and probably extreme examples at that, but it does illustrate the difference in damage a rifle round vs a pistol round can potentially cause.

That variability is exactly why I posited this question. Definitely seen a good number of GSWs, but also remember the Fackler report on how unimpressive 5.56mm wounds were, absent fragmentation or yaw. That M193 injury was devastating because of the fragmentation which we know creates the larger wound cavity. Again though, still haven't seen a single wound illustration or picture that shows a non-fragmenting bullet TC creating a wound larger than the expansion.

So, IF these are correct:
1. Pistol HPs usually will expand to a greater diameter than their rifle counterparts, while still maintaining 12 inches of penetration.
2. We must destroy vital tissues or cause significant blood loss. Since TC isn't some magical unicorn shockwave, it must destoy tissue like the PC to be at all useful.
3. Our target area is highly resistant to TC.

Then why are rifle bullets much more effective?