Terminal ballistics

A Brief Guide To Terminal Ballistics

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But the quantity of kinetic energy alone does not tell us enough to predict the dimensions of this cavity. Reality differs. Real bullets generally deform and real tissue is extremely elastic. In understanding the interaction of the bullet with the target, it is helpful to consider the water analogy. The higher the impact velocity of a projectile, the greater the initial resistance. This is what I call the "splash effect", and is true of all solids when the stresses placed upon them overcome their intrinsic rigidity and cause them to behave like a fluid. It is easier to push your hand into water than to slap into it.

Pushing slowly, you can penetrate deeper with less effort energy than by slapping at a high velocity.

However, by slapping you make a bigger splash in the water cavitation. These are exactly the basic mechanisms which govern terminal ballistics in living tissue. Understanding how the kinetic energy of a bullet contributes to wounding, we can consider the separate components of wounding.

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Mechanics of Penetration Penetration is simply the depth to which a bullet passes through a target. Factors affecting penetration for modern weapons, in order of importance are: 1 bullet construction, 2 bullet shape, and 3 impact velocity. In general terms velocity is the most important factor, but most rifle cartridges develop similar velocities, so within this typical range of interest, as we will see, other considerations prove more significant.

Bullet construction is the most important factor because it will determine whether the stresses of impact allow the bullet to overcome the resistivity of the target. In other words, is the bullet tough enough to survive the impact and penetrate, or will it shatter, and if so, how far will the fragments penetrate? Advances in metallurgical processing of bullets have made contemporary designs superior to anything used in the last century, giving small-bore bullets the effectiveness of huge lead balls.

The target material will greatly affect the selection of bullet material, but in general, toughness malleability is more important than hardness. Other features, such as bonded cores and tapered or partitioned jackets permit greater penetration by controlling the expanded presented area and retaining bullet mass.

Bullet shape is next in importance because a pointed bullet which does not deform becomes unstable at impact velocities of interest and will not penetrate as deeply as a flat-nosed or round-nosed bullet of the same weight and velocity. Non-deforming round nosed bullets generally penetrate more deeply than flat-nosed bullets, depending on the width of the flat nose and the radius of the round nose. Since nearly all rifle bullets today are pointed designs intended to deform, bullet shape also applies to expanded or fragmented bullets.

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Sectional density is bullet weight divided by the diameter squared. In simplistic theory, it describes the relative ability of a bullet or fragment to penetrate. For a given caliber, the heavier bullet will have a higher sectional density. However, this value does not consider bullet construction, the shape of the nose or the effect of ablation loss of bullet mass.

At impact, the effective sectional density becomes the retained bullet weight divided by its expanded represented frontal area which initially is smaller than the nominal caliber. Thus, practically speaking, two bullets having the same sectional density can have very different penetrations after impact, depending upon their shape and toughness. Sectional density is a misleading indicator of performance for bullets of different constructions and materials; sometimes even for apparently similar designs.

Varmint bullets have low sectional densities, but even these values suggest better penetration than they are capable of providing when compared to big-game bullets of heavy jacketed, bonded core or monolithic construction. Similarly, the stronger premium bullets such as the Barnes X-Bullet are capable of penetrating as deeply as bullets of conventional construction having much higher sectional density.

Finally, impact velocity determines the hydrodynamic pressure, which may be thought of as the resistance to penetration encountered by the bullet. Impact velocity has a significant effect upon bullet deformation involving both bullet construction and shape , but beyond this it also affects the amount of cavitation caused by the bullet in tissue.

In theoretical terms, a projectile creates a cavity which is proportional to its kinetic energy actually, the permanent volume of the cavity may be considerably less than the theoretical expected volume. The cavity extends radially what I term cavitation and along the path of the bullet penetration.

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The more it cavitates, the less deeply it penetrates. High velocity can have a detrimental effect upon penetration in a fluid, due to the "splash effect". It can destroy the bullet or cause it to create an enormous cavity without penetrating which is not necessarily undesirable in certain tactical situations.

Most rifle bullets are designed to perform reliably within a rather narrow range of velocities, usually to fps for most conventional rifle bullets. Below this velocity range, the bullet may not expand; above it, the bullet may shatter on impact. This is a limitation imposed by material properties and design characteristics. For this reason, bullets which are intended for pistol hunting loads would be inappropriate for use in high velocity rifles, since their impact velocities would be very much higher than those they were designed for although they may perform perfectly for long range shots where the velocity has moderated.

Other bullets, referred to as "custom" or "premium" designs, can be successfully used for a wider range of impact velocities, perhaps as low as fps and as high as fps though most designs tend to work better at one end of the velocity spectrum than the other.

They are typically designed to expand easily at low velocities but retain their weight at least most of it at high impact velocities. Bullets designed for the older low-velocity rifle cartridges and for handguns can be relied upon to expand down to about fps in the case of rifles and fps in handguns. Against hard solid targets, such as armor or heavy bones, high impact velocity is the most important factor contributing to maximum penetration assuming that the bullet remains intact , because this has a shattering effect upon the material.

Maximum penetration in a fluid medium, however, is achieved when cavitation is held to a minimum, as in the case of a non-deforming, round-nosed bullet travelling at "moderate" velocity. Heavy big-bore, flat-nosed, hard-cast lead-alloy bullets are favored by handgun hunters for large game because they are more efficient than jacketed soft points.

The broad flat nose on the relatively large caliber bullet provides adequate cavitation, so expansion isn't necessary. Since there is no expansion, there is also no energy lost to bullet deformation - all of the remaining kinetic energy of the extra-heavy bullet is directed toward penetration with acceptable cavitation. The course will include both classroom presentations and live fire range exercises. This course will conclude with a Course Review and Examination. All instruction materials, range time, and targets are provided by Tactical Services Group.

A surgeon's judgment and his technique of tissue excision is very subjective, as shown by Berlin et al 66 , who found in a comparison that "One surgeon excised less tissue at low energy transfers and rather more at high energy transfers than the other surgeon, although both surgeons used the same criteria when judging the tissues. Interestingly, all studies in which animals were kept alive for objective observations of wound healing report less lasting tissue damage than estimated from observation of the wound in the first few hours after it was inflicted , 67, In a study of over 4, wounded in WW II it was remarked, "It is surprising to see how much apparently nonvital tissue recovered" Anyone yet unconvinced of the fallacy in using kinetic energy alone to measure wounding capacity might wish to consider the example of a modern broadhead hunting arrow.

It is used to kill all species of big game, yet its striking energy is only about 50 ft-lb 68 Joules -- less than that of the. Energy is used efficiently by the sharp blade of the broadhead arrow. Cutting tissue is far more efficient than crushing it, and crushing it is far more efficient than tearing it apart by stretch as in temporary cavitation. Duct-sealing compound 73 , clay 2,74 , soap 66, 72 , gelatin , 38 , and water-soaked phone books or newspapers 74 are commonly used tissue simulants. Information from each has been presented in the literature with the implication that it yields valid predictive information about wounding effects in living animals.

Contrary to the assumptions that these materials are equivalent to animal tissue, bullet deformation caused by impact with them can vary widely. Nonelastic tissue simulants duct-sealing compound, clay, soap can also mislead by their dramatic preservation of the maximum temporary cavity.

Wound Ballistics: A Bullet’s Life on the Inside, By Mike McTee

Such demonstrations give a false impression that these cavities represent the potential for tissue destruction rather than the potential for tissue stretch. The latter may be absorbed by most living tissues with little or no lasting damage. In the battlefield setting the surgeon cannot know, with certainty, all the properties of the wounding projectile shape, mass, construction type, striking velocity.

In a majority of civilian cases information about the wounding weapon is not available Fortunately, such information is not necessary for the proper treatment of gunshot wounds. In fact, it is the author's opinion that the patient will be better off if his medical care provider doesn't know anything about the wounding weapon at all. The provider might then, without bias, use objective data from his physical examination and roentgenographic studies to make more valid treatment decisions.

When a penetrating projectile does cause significant tissue disruption, that disruption is usually very obvious. For example, in an uncomplicated extremity wound caused by the M rifle Fig 2 , if the bullet yaws significantly and fragments, this will be evident in the form of a large exit hole. If no significant yaw occurs, the exit will closely resemble the entrance hole, and little or no functional disturbance will be evident because of minimal tissue disruption.

Terminal Ballistics

If, on the other hand, the bullet breaks up very early in its path through the tissue, it is possible that the entrance and exit holes could be small despite marked tissue disruption within the limb such a pattern is typical of a soft point bullet Fig 7 ; occasionally this pattern may also be produced by the M bullet. The situation should pose no diagnostic problem; marked functional disturbance with swelling will be obvious on physical examination, and the bullet fragmentation with soft tissue disruption will be obvious on biplanar x-rays.

As in the therapy of any other form of trauma, objective data should guide treatment decisions. The author was consulted recently about a case in which gas gangrene had developed in a leg wound caused by a. Surgical exploration of the wound had been delayed until 40 hours after the injury, and the first antibiotic had been administered four hours after the operation. It was the author's opinion that treatment had been inappropriate, but could not be considered negligent, since the literature contains many recommendations such as " If antibiotic coverage had been started soon after the wound occurred, and if the bias obtained from the literature had not misled the surgeon to delay surgical exploration of the wound, this lethal infection most certainly would have been avoided.

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Light bullets of high velocity lose velocity rapidly in flight--a basic physical phenomenon Perhaps the aforementioned weapon problems could have been avoided if weapons designers had been less influenced by the mystique of "high velocity" and more influenced by basic physics of projectiles in flight. They might have realized that the older M bullet was too light to be effective at longer ranges and used a heavier bullet in the first place. It is difficult to be optimistic for the future when these weapons developers still use the scientifically discredited "kinetic energy deposit" method to estimate wounding effects.

An extensive body of misinformation has been promulgated 28,29 , based on the assumption that the temporary cavity produced by a handgun bullet is the sole factor determining its "incapacitation" effect on the human target. These studies were done to aid law enforcement agencies in their choice of weapons.

The investigators superimposed temporary cavity measurements, derived from shots into gelatin blocs, on a computer man" diagram of the human body. They judged relative damage by the anatomic regions "included" in the cavity. A "Relative Incapacitation Index" for each bullet was then calculated from these data.

The superimposition of the temporary cavity on a region to determine the anatomic structures it encompasses reveals a serious misunderstanding of wounding mechanisms. By definition, no tissue is included "in" the temporary cavity: tissue is pushed aside by it. Using the permanent cavity in this fashion would make sense, but the permanent cavity is totally ignored in the calculation of the Relative Incapacitation Index. Not surprisingly, this Relative Incapacitation Index has been criticized 17, 79, 80 , but reliance on its supposed validity continues to endanger the lives of those who must depend on the reliable performance of their weapon.

Of Justice , causing many to assume their validity, and compounding the detrimental effects of the misinformation. Misinterpretation of war trauma experience has misled many writers. Such experience is anecdotal.

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