BigMak said:
Michael,
I'm specifically interested in your assessment
of MacPherson's statements about temporary
wound cavity (p.58-63), and particularly your
input as to why his explanation of kinetic energy
not being a main factor in wound trauma
incapacitation is invalid.
MacPherson's unstated presuppostion that incapacation can only result from wound trauma that is easily detected by a medical examiner or trauma surgeon is unproven. The assertion that kinetic energy is not a main factor in incapacitation rests on this unproven presupposition.
Kinetic energy dump (dE/dx) is a main factor in both the magnitude of the ballistic pressure wave and in the temporary stretch cavity. Much of the work we have in preparation for publication is greared toward correlating the ballistic pressure wave to incapacitation without much concern for the physiological mechanisms involved. We have only recently begun a new research project to associate wounding with the pressure wave.
Because of the high correlation between the temporary cavity and the pressure wave magnitude, we cannot conclusively rule out the temporary cavity as an important contributor to incapacitation. The pressure wave correlates a bit better to incapacitation than the temporary stretch cavity, but it is not conclusive.
However, we can say that we need to consider more than the permanent crush cavity alone to get a good correlation with incapacitation. A model which includes both PCC and TSC gives good correlation, and a model using PCC and the pressure wave magnitude is slightly better. Combined with our experiments showing incapacitation of 10-20 lb mammals with only a pressure wave (no PCC or TSC), we believe we have significant supporting evidence for the pressure wave.
I don't wish to be overly critical of other researchers or their contributions. In fairness to other researchers, we are concentrating on handgun loads that produce pressure waves considerably larger than commonly showing up in the morgue or operating table. The majority of handgun loads may well fail to produce pressure wave/TSC wounding that is easily detectable, and even the most careful study that concentrates on wounding rather than a quantifiable metric of incapacitation might miss the effects we are seeing.
BigMak said:
I guess what I'd like to hear from you is where
specifically do you find that his tests/viewpoints
are invalid, both in the areas of kinetic energy
effect and, also, temporary cavity elasticity.
In addition to the unproven presupposition that all the contributions to incapacitation are easily detectable wounding, another problem is over generalization of conclusions based on wounds from bullets with relatively low pressure waves (energy dump, dE/dx) to bullets with considerably higher pressure waves. This is an overgeneralization that readers tend to add to the idea, rather than something written explicitly.
The case regarding temporary cavity elasticity has some weak areas. It is true that some tissues have a higher tolerance than others for stretch, so the effect of the TSC depends on the internal organs within reach of the TSC. But there is another factor in play: tissue failure depends not only on the degree of stretch, but also on the rate of stretch. A tissue that can tolerate being stretched a given amount at a relatively slow rate will often tear if stretched the same amount at 50-100% faster rate. Elasticity is no guarantee against wounding as the rate of energy transfer is increased. In other words, tissue that can tolerate a stretch of 3" delivered by a load that transfers 350 ft-lbs of energy in 12" of penetration might fail if delivered the same 3" of stretch by a load that transfers 550 ft-lbs of energy in 12" of penetration.
Let me be clear that I do not believe that MacPherson's conclusions are not supported by his observations. He might simply not have considered consider incapacitation apart from easily detectable wounding, and he might not have had ample opportunity to observe wounding and incapacitation from the handgun loads with both substantial penetration (>10") and pressure waves above 1000 PSI (on the surface of a 1" diameter circle centered at the wound tract.) It is not valid to extrapolate his observations to effects of loads with considerably larger pressure waves. I think that the readers have a greater propensity for this unwarranted extrapolation than the author.
Professionals in the wound ballistic field who consider incapacitaion apart from detectable wounding need to have other career options. It's hard to find fault with researchers who stick with the unproven presupposition that incapacitation only results from easily detactable wounding, but I think the presupposition is wrong, and investigating how it might be wrong is an important step in improving terminal performance of handgun bullets.
Michael Courtney