The Ballistic Pressure Wave Theory of Handgun Bullet Incapacitation
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The Ballistic Pressure Wave Theory of Handgun Bullet Incapacitation Michael Courtney, PhD Ballistics Testing Group, P.O. Box 24, West Point, NY 10996 [email protected] Amy Courtney, PhD Department of Physics, United States Military Academy, West Point, NY 10996 [email protected] Abstract: This paper presents a summary of seven distinct chains of evidence, which, taken together, provide compelling support for the theory that a ballistic pressure wave radiating outward from the penetrating projectile can contribute to wounding and incapacitating effects of handgun bullets. These chains of evidence include the fluid percussion model of traumatic brain injury, observations of remote ballistic pressure wave injury in animal models, observations of rapid incapacitation highly correlated with pressure magnitude in animal models, epidemiological data from human shootings showing that the probability of incapacitation increases with peak pressure magnitude, case studies in humans showing remote pressure wave damage in the brain and spinal cord, and observations of blast waves causing remote brain injury. I. Introduction 3) Experiments in animals showing the Debates in terminal ballistics such as light-and- probability of rapid incapacitation increases fast vs. slow-and-heavy debates are dramatic with peak pressure wave magnitude [STR93, oversimplifications of the more scientific COC06c, COC06d, COC07a]. question of whether the wound channel (directly 4) Epidemiological data showing that the crushed tissue) is the only contributor to probability of incapacitation increases with the handgun bullet effectiveness or whether a more peak pressure wave magnitude [MAS92, energy dependent parameter such as MAS96, COC06b]. hydrostatic shock, the temporary stretch cavity, 5) Brain damage occurring without a or ballistic pressure wave can also contribute. penetrating brain injury in a human case study [THG96, COC07b]. These debates have been dominated by long- 6) Ballistic pressure waves causing spinal cord winded rhetoric and authoritative appeals rather injuries in human case studies [STU98, than scientific data and analysis. Here, we SSW82, TAG57]. summarize findings that support and quantify 7) Blast waves causing brain injury without the pressure wave hypothesis: penetrating injury or blunt force trauma [MAY97, TAH98, CWJ01]. Other factors being equal, bullets producing larger pressure waves incapacitate more rapidly than bullets producing II. What is the ballistic pressure wave? smaller pressure waves. The ballistic pressure wave is the force per unit area created by a ballistic impact that could be The pressure wave hypothesis is supported by: measured with a high-speed pressure 1) Pressure pulses inducing incapacitation and transducer [COC06c]. The bullet slows down brain injury in laboratory animals [THG97, in tissue due to the retarding force the tissue TLM05]. applies to the bullet. In accordance with 2) Ballistic pressure waves originating remotely Newton’s third law, the bullet exerts an equal from the brain causing measurable brain injury and opposite force on the tissue. in pigs and dogs [SHS87, SHS88, SHS90a, SHS90b, WWZ04]. 1 The average pressure on the front of a bullet is kinetic energy is the same. However, the the retarding force divided by the frontal area of potential for increased incapacitation is limited, the bullet. The pressure exerted by the medium because the wave must be created inside soft on the bullet is equal to the pressure exerted by tissue and close to major blood vessels or vital the bullet on the medium. Because the frontal organs to have its effect. A bullet that barely area of a bullet is small, the pressure at the penetrates the thoracic cavity has little effect. front of the bullet is large. Incapacitation effects are reduced for penetration depths below 9.5 inches Once created, this pressure front travels [COC06b]. outward in all directions in a viscous or visco- elastic medium such as soft tissue or ballistic III. Fluid Percussion Model of TBI gelatin. Propagating outward, the wave’s The lateral fluid percussion model (LFP) of decreasing magnitude results from the traumatic brain injury (TBI) is used to study increasing total area the pressure wave covers. mechanisms of traumatic brain injury [TLM05]. A brief pressure pulse is applied directly to the To compare pressure waves produced by brain of a laboratory animal. different loads, it is necessary to specify the distance from the center of the bullet path. For Both instantaneous incapacitation and neural non-fragmenting JHP handgun bullets that damage can result [THG97]. Investigators expand reliably, the peak pressure wave have shown mild and moderate injury levels magnitude (in PSI) on the edge of a 1” diameter occur with pressure levels in the 15-30 PSI cylinder concentric with the bullet path can be range. Pressure waves near 30 PSI caused estimated as [COC06c] immediate incapacitation in laboratory animals. It is widely believed that this model has direct 5E application to cellular and mechanistic effects p , d of TBI in humans [TLM05]. where E is the kinetic energy (ft-lbs) of the IV. Animal models of remote brain injury bullet at impact, and d is the penetration depth Suneson et al. [SHS87, SHS88, SHS90a, (feet). The pressure wave is larger for SHS90b] implanted high-frequency pressure fragmenting bullets [COC06b]. transducers into the brains of pigs to measure pressures generated by missile impacts in the Wave magnitude falls off with increasing thigh. Transient pressure levels in the 18-45 distance from the point of origin unless reflected PSI range were transmitted to the brain by a boundary or confined to an internal [SHS90a, fig 1]. structure. An internal pressure wave created in the thoracic cavity will be reflected multiple Early tests [SHS87] observed apneic (non- times by the sides of the cavity. Superposition breathing) periods after injury. Tissue analysis of waves creates localized regions of high showed damage to brain-blood and blood- pressure by focusing the wave, just as concave nerve barriers. Subsequent experiments mirrors focus light waves and concave surfaces [SHS90a, SHS90b] reported damage at the focus sound waves. cellular level in the hippocampus and hypothalamus regions of the brain. This Since pressure wave magnitude is inversely damage was apparently caused by pressure proportional to penetration depth, cutting waves transmitted to the brain from the distant penetration in half doubles the pressure, if (0.5 m) point of origin. 2 coefficient of R = 0.91. A plot of AIT(p) is Martin Fackler, former editor of the out of print shown in Figure 1 along with the data. Wound Ballistics Review, published negative reviews of these findings [FAC91a, FAC96a]. Average Incapacitation Time vs. Peak Pressure Wave Magnitude However, his critical reviews have been shown 50 to contain exaggerations, logical fallacies, and 45 scientific errors [COC06a]. 40 35 ) For example, Fackler asserts that Suneson's s d 30 n o findings are invalid because lithotripsy c e s 25 ( (ultrasonic kidney stone treatment) applies a e m i 20 large pressure wave without damaging tissue. T However, pressure waves associated with 15 lithotripsy have been shown to cause significant 10 tissue injury [EWL98, LOS01, LKK03]. 5 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 In addition, remote brain injury attributed to a Pressure (PSI) ballistic pressure wave has also been found in a Figure 1: A plot of average incapacitation time vs. pressure similar experiment in dogs. Independent for the Strasbourg tests, along with the best-fit model. scientists concluded [WWZ04]: Fackler has also criticized this data set These findings correspond well to the results of Suneson et al., [FAC94a, FAC97a]. Without any eyewitness, and confirmed that distant effect exists in the central nervous documentary, or physical evidence showing system after a high-energy missile impact to an extremity. A fraud, he uses the opinion of a group of experts high-frequency oscillating pressure wave with large amplitude and short duration was found in the brain after the extremity to assert that the report is fraudulent [FAC94a]: impact of a high-energy missile . The FBI committee, which includes a half dozen of the world’s These animal models provide compelling most highly regarded gunshot-expert forensic pathologists, felt support for the pressure wave hypothesis. that the organization and wording of the document betrayed it as a hoax. Why else would experimental results be circulated anonymously? V. Animal models of incapacitation The largest available data set quantifying In a self-contradiction, these six "experts" are handgun bullet incapacitation in animal test not named. The FBI committee remains subjects (goats) [STR93] shows that average anonymous while stating anonymity as the incapacitation time correlates strongly with criterion used to determine that the Strasbourg ballistic pressure wave magnitude [COC06c]. report is a hoax!1 A model for average incapacitation time in Fackler’s review also contains numerous terms of peak pressure wave magnitude, p, is: fallacies leading a review to conclude [COC06a]: p AIT( p) 10s 0 , p In the absence of support or direct contradiction from other experiments, the veracity of the Strasbourg tests should fairly where p0 is an adjustable parameter that gives an average incapacitation time of 10 seconds. 1 In the history of science, there are a number of examples of A least-squares fit gives p0 = 482 PSI with a anonymous publication. Anonymity is not generally considered standard error of 1.64 s and a correlation a conclusive indication of fraud [COC06a]. 3 be considered to be an open question. Neither the anonymity of combined by the rules of probability to derive a the authors nor other criticisms offered are sufficient to model for the total OSS rating. consider the report fraudulent. Rather than lean too heavily on (possibly biased) expert opinions, the veracity of the report should be determined by the degree to which the reported The OSS model can be written as results find support in other experimental findings.