What Is “Shock”, and Should It Be a Primary Terminal Performance Consideration When Selecting a Hunting Cartridge?

By Scott Fletcher

“The first step in validating Chicken Little’s claim that the sky is falling is to determine if it’s raining.”  -  Scott Fletcher

The answer to the question posed by the article’s title is “no”.

An animal instantaneously dropping with a shot other than to the spine or brain is attributed to “hydrostatic shock” by virtually all hunters. The typical reason presented is that the reaction is caused by the rapid release or transfer of kinetic energy. This energy release is commonly alleged to result in shock waves that are transmitted through tissue fluids that switch off the central nervous system. A progressively higher bullet impact energy is commonly thought to progressively increase the frequency of a drop-to-the-shot reaction.

I can find no scientific/authoritative papers that satisfactorily explain the physiological mechanisms/process responsible for this reaction, nor how this reaction is triggered by passage of a projectile. I have not found a published, authoritative paper that presents any mathematical or empirical relationship between a bullet’s impact energy and its ability to produce “shock” with an attendant drop-to-the-shot reaction, nor can I find a medical or veterinary science publication that has a definition of “shock” that includes such a reaction. Simply stated, if there is no authoritative, scientific reason for how this reaction is caused, there can be no authoritative, scientific justification nor validation of its occurrence.

This article presents an engineer’s interpretation of how “shock” is produced in a game animal, how it apparently affects its body, and the relationship of its occurrence to a bullet’s impact energy. These interpretations are based on both field and skinning-shed observations made during the 2023 management hunt, applicable information contained in published articles concerning “shock”, and valid geotechnical engineering concepts. The intent is to distill this information into practical advice hunters can use.

What will be described is not static, not even close. In the civil engineering profession, the word “hydrostatic” means constant, or nearly constant, water pressure. Using this word to describe “shock” makes no sense because the passage of an expanding hunting bullet through tissue causes a violent, rapid, and transient pressure spike in the surrounding blood. This blood-pressure spike and its adverse effect on actual tissue and the animal’s involuntary nervous system are assessed to be the primary triggering mechanisms for the animal reaction of drop-to-the-shot hunters call “hydrostatic shock”. Consequently, the phrase chosen to describe and define this process is hydrodynamic shock.

Hydrodynamic Shock definition: Hydrodynamic shock is a physiological process that produces variable, involuntary debilitation of both muscle and critical, life-support organs up to and including failure.

So, what is this process? A bullet entering and passing through tissue both destroys and displaces it. In addition to mechanically wrecking the cells it directly passes through, the bullet also displaces adjacent cells and the blood within these cells. Blood is incompressible, and it forces its way into adjacent cells trying to “make room” for the volume displaced by the bullet. Even though the adjacent cell membranes are porous and elastic, they simply are not porous nor elastic enough to accommodate the rapid volume increase of blood displaced by the bullet. The adjacent cells then rupture in response to this blood-pressure spike, causing what hunters know as bloodshot meat.

This blood displacement radiates away from the bullet’s path, creating a blood compression wave. The blood pressure within this compression wave is abnormally high. Even though the pressure within the wave dissipates from progressive elastic expansion and permeation through cells farther and farther away from the bullet’s path, it can still get transmitted directly to the brain via the circulatory system with potentially enough pressure to mechanically rupture delicate cerebral blood vessels, potentially debilitating the brain sufficiently to cause a drop-to-the-shot reaction.

This abnormally high blood pressure within the circulatory system could also trigger the “fight or flight” reaction in the nervous system that is hard wired into the non-cognitive, involuntary response portion of the brain. The violence of the blood-pressure spike in the circulatory system is thought to be piezo-electrically transmitted to the nervous system and then to the brain by the vagus nerve. The vagus nerve is connected directly to the heart, and has multiple nerve endings in the respiratory area of the lungs. Thus, a bullet through the boiler room can transmit an immediate, uber-defensive condition through the circulatory system to the brain via the nervous system. The involuntary portion of the brain that serves as the receptor to this nervous-system stimulus tries its best to accommodate this “crimson alert” with such things as an adrenalin dump and instantaneous muscle contraction to initiate “fight or flight”.

This involuntary “fight or flight” response of the animal is assessed to cause a progressive degree of muscle-contraction violence that can be sufficient to induce another spike in the blood pressure of the animal. As with the blood-pressure wave directly induced into the circulatory system by passage of the bullet, this blood-pressure-induced spike from violent muscle contraction can get transmitted directly to the brain via the circulatory system where it can also mechanically rupture delicate cerebral blood vessels, producing a drop-to-the-shot reaction. 

Evidence of progressive muscle contraction assessed to be violent enough to produce such an extraordinary blood-pressure spike was observed on numerous animal carcasses during the skinning-shed autopsies conducted during the referenced hunt. This evidence was in the form of point-source “blood pimples” emanating from muscle tissue at various locations on the carcass. This muscle contraction was apparently violent enough to produce blood pressure sufficient to rupture the muscle cells that produced it, as indicated by this point-source bleeding. These point sources of bleeding were visible both on the muscle tissue itself and in attendant, blood-impregnation staining of the adjacent hide. The fact that the hide, itself, was bloodstained further underscores the extraordinary degree of pressure in the circulatory system caused by this involuntary nervous system response. This muscle tissue-bursting response is defined as blood hammer (BH).

Photo P-42 shows Zebra Z-5 in the process of being skinned. The BH is indicted by the irregular, circular blood splotches/staining on both the carcass and the hide in the shoulder and the neck area. The bullet entrance hole is visible behind the shoulder. Photo P-43 is also of Zebra Z-5, and shows BH on the hide, the rear haunches, and the spine. With time, these ruptures in the muscle tissue freely weep blood, as indicated by Photo P-44. This photo is of the neck and the shoulder area of Zebra Z-2.

The blood shown in the previous photos has NOT been caused by the skinning process, as indicated by neck and shoulder portions of both the hide and the carcass identified in Photo P-42, and the rear haunches and the spine-portion of both the hide and the carcass shown in Photo P-43. The staining occurrence and the shape of the stain indicate the hide had been stained with blood before the skinning had been begun.

Photo P-45 is of Zebra Z-3 and underscores that the staining of the hide occurs in response to blood hammer rather than inadvertent tissue slicing from the skinning process.  The picture shows a skinned carcass with virtually no bleeding either from the skinning process or the blood hammer.

The multiple carcasses observed throughout the hunt indicated an apparent progression in the severity of BH, suggesting a progression in the severity of shock. If BH occurred, it tended to be first evident on the neck, as shown in Photo P-46 (Zebra Z-4). As the inferred shock severity increased, the next portion of the carcass affected appeared to be centered along the spine. Subsequent increases in inferred shock intensity were indicated by BH spreading first to the shoulders, then to the rear haunches, as indicated in Photo P-47 (Zebra Z-5). The most severe interpreted degree BH affected the neck, the back, the shoulder muscles, and the rear haunches of the carcass.

The degrees of adrenalin, respiratory rate, and power stroke of the heart are all variables that can conceptually affect the actual magnitude of the blood pressure in the animal at the time of bullet impact. As indicated by BH, stimulation of the involuntary nervous system associated with the vagus nerve could potentially produce varying degrees of muscle contraction that also likely contribute to a variability in blood pressure. The total variability in the blood pressure from the degree of adrenalin, respiratory rate, power stroke of the heart and involuntary muscle contraction all potentially results in variable debilitation of the animal, with the debilitation threshold of drop-to-the-shot apparently not easily achieved.

Rather than piezo-electric stimulus from the circulatory system triggering violent, involuntary muscle contraction, direct mechanical disruption of the nervous system can also apparently trigger this contraction. Photo P-51 shows the exit neck wound of Zebra Z-4 where the bullet completely severed its vertebrae. Note the blood “weeping” from its eye, potentially indicating bursting of brain cells. Photo P-52 shows Zebra Z-4 being skinned, with BH on the neck freely weeping blood.

Zebra Z-6 is the only animal on the management hunt judged to have exhibited a dropped-to-the-shot reaction attributed to hydrodynamic shock, as defined by this article. The bullet impact energy causing this reaction was the ninth lowest (next to last) of all the kill spots made on the hunt. (Refer to Table 4) Its carcass exhibited significant BH indicative of a high degree of hydrodynamic shock on its neck, shoulder, spine, and rear haunches. Photo P-48 shows BH on the back, the haunches and the carcass shoulder of Z-6; Photo P-49 shows BH on the neck and shoulder of Z-6; and Photo P-50 shows BH on the spine, the back, and the haunches of Z-6.

Zebra Z-9 had the highest kill-shot bullet impact energy of all kill spots made on the hunt. As indicated by Table 4, its impact energy was about 23% greater than the impact energy recorded for Z-6. Both zebras were shot with the same bullet. Photo 1 is of Z-9’s back, shoulder, and haunches, and is comparable to Photo P-48 of Z-6; Photo 2 is of Z-9’s shoulder and neck, and is comparable to Photo P-49 of Z-6; and Photo 3 is of Z-9’s spine, back and haunches, and is comparable to Photo P-50 of Z-6.

Photos 1, 2, and 3 show there is no-to-limited occurrence of BH on Z-9’s carcass compared to Z-6’s carcass. This lack of BH indicates that minimal hydrodynamic shock, as defined by this article, occurred. If the degree of hydrodynamic shock is directly/proportionally related to bullet-impact energy, the 23% increase in bullet-impact energy associated with Z-9’s kill shot should have produced BH that was noticeably greater than Z-6’s. The significant decrease in BH on Z-9 compared to Z-6 indicates there is no apparent “logical”, direct, and proportional relationship between a bullet’s impact energy and its ability to produce hydrodynamic shock. Because there is no apparent relationship between a bullet’s impact energy and its ability to produce hydrodynamic shock, there is also no apparent relationship between a bullet’s impact energy and its ability to produce the attendant, drop-to-the-shot reaction.

Bottom Line: the physiological mechanism(s) causing shock, by any definition, from an expanding hunting-bullet wound is (are) likely primarily embedded in blood-pressure compression wave and blood/cell piezo-electric principles. The factors causing animal debilitation from shock are likely caused by the interaction of both the circulatory and the nervous system. These factors are highly variable, based on the animal’s physiological condition at the exact instant of bullet impact as well as the exact impact location of the bullet. This variability produces a corresponding variability in debilitation. Consequently, a drop-to-the-shot animal reaction, strictly from “shock”, is simply an infrequent luck-of-the-draw.

The foregoing assessment is at odds with what virtually all hunters “know” to be true based on field observations. For example, the impact of a 30-caliber, 150-grain, cup-and-core bullet launched from a magnum chambering into the boiler room of an animal such as a southern white tail or impala typically causes a drop-to-the-shot reaction. If a drop-to-the-shot reaction from “shock” is an infrequent, luck-of-the-draw occurrence, then what is the primary cause of this reaction?

Based on the results obtained on the management hunt and the conclusions presented in the wound-cavity-volume article, the reason is simply based on the magnitude of wound cavity volume produced by the chambering/bullet combination. The engineering rationale and data justification are presented in the article entitled “If an Animal’s Drop-to-the-Shot Reaction from “Shock” Is Luck-of-the-Draw, What Is the Terminal Performance Sure Bet?”