Understanding bullet impacts.
Terminal Ballistics – Part I is the first in a two-part series which will begin to conclude the Ballistics Series by introducing the principles within Terminal Ballistics and focus on the various aspects of projectile impacts on target and their immediate effects. Leveraging the key concepts of projectile flight and construction, momentum and kinetic energy introduced earlier in the ballistics series, this article will illuminate some scientific facts in regard to the terminal effect of firearm employment for hunting, law enforcement and personal defense while also debunking some commonly-held myths. In researching this topic, I’ve relied heavily on authoritative sources such as Robert Rinker’s “Understanding Firearm Ballistics, 6th edition,” and the Federal Bureau of Investigation’s 1989 report titled “Handgun Wounding Factors and Effectiveness.”
Whether for recreation, competition, training, hunting or personal defense, this ballistic series has focused on the myriad of aspects that affect a projectile’s flight to target in order to provide a better understanding and help you choose the right firearm/ammunition combination to safely and consistently place your shots on target and achieve the desired ballistic effects. From the mechanical interactions internal to the firearm to the atmospheric and physical conditions that affect projectile flight, this series has provided information necessary to harness mechanical precision into shooter accuracy. Now, we will discuss projectile impacts on target.
Since recreational and competitive shooters are primarily focused on measuring the effectiveness of their skill and technique by scoring shots on paper, cardboard, or interactive targets, terminal ballistics is simply a factor of hitting the target for score. For hunters, military/law enforcement, and personal defenders, on the other hand, the projectile’s ultimate effect is eminently important since it is the sole reason for weapon employment. Although the conditions for weapon employment are much different in these latter cases, the desired result is the same… rapid incapacitation with as few shots fired as possible!
This rapid incapacitation is a factor of shot placement combined with velocity, kinetic energy, projectile weight, projectile shape and construction, caliber, and range to target as well as the nature of the target itself. In order to move forward with the discussion, we need to first discuss some terms and concepts common to both hunting and personal defense.
Terms and Concepts
- Caliber – diameter of a projectile
- Mass – in the most general terms, this is the weight of the projectile
- Velocity – this is the instantaneous speed at which the projectile is moving. Projectiles exit the firearm bore with an initial velocity which immediately begins to slow down due to air resistance and drag.
- Ballistic Coefficient – based on the shape and construction of the projectile, this number describes how well the projectile travels through the air and preserves its velocity.
- Momentum – this is calculated as the projectile’s mass times the velocity (M*V). Keep in mind, as the shot is fired, impulse (or recoil) is caused by the force required to accelerate the projectile through the bore. At all points along the projectile’s travel to target, the projectile maintains a constant mass, but its velocity is diminishing, so its momentum decreases along the trajectory. When the projectile impacts the target, it imparts its residual momentum on the target which is absorbed by the target itself. This is a good time to dispel the myth proffered by Hollywood… no firearm projectile can “knock down” a human or animal target through momentum alone. Even at close range, the transfer of momentum, or force, into the target CANNOT exceed the force from the point of origin (which is impulse/recoil). Even if it was possible to knock the target down through projectile momentum, the force required would also knock down the shooter.
- Kinetic Energy – this is calculated as one-half of the projectile’s mass times velocity squared (1/2*M*V²). Energy, expressed in foot-pounds, describes an object’s ability to do work or transfer that energy into another object. An object with 2,000 ft-lbs of energy can raise another 2,000lb object 1 foot. Don’t let the size of the numbers fool you. A 175 grain .308 caliber round traveling at 2,762 feet per second possesses 2,965 foot-lbs of energy, which theoretically would move a 2,965 pound object 1 foot or a 1 pound object 2,965 feet. However, this describes a 1-to-1 transfer of energy (i.e. no penetration), which is not the case when a projectile impacts a body. When the projectile does impact a body, the energy is consumed during the process of penetration and passing through layers of tissue and fluid that absorb the energy.
- Penetration – based on diameter, shape, and momentum, this describes the projectile’s ability to disrupt or destroy tissue as it passes through.
- Permanent Wound Cavity – “the volume of space once occupied by tissue that has been destroyed by the passage of the projectile.” (Source: FBI)
- Temporary Wound Cavity – “The expansion of the permanent cavity by stretching due to the transfer of kinetic energy during the projectile’s passage.” (Source: FBI)
- Fragmentation – “Projectile pieces or secondary fragments of bone which are impelled outward from the permanent cavity and may sever muscle tissues, blood vessels, etc., apart from the permanent cavity. This is to be considered a secondary effect.” (Source: FBI)
- Kinematic Viscocity – Since human and animal bodies are composed mostly of water, and water is considered incompressible, the high velocity impact of a projectile will cause a dramatic hydraulic action imparting shock-waves among the blood vessels and body parts in the vicinity of the impact. In general terms, higher velocities impart greater explosive effects and velocities of at least 3,000 feet per second (ft/s) are required for true hydrostatic shock.
Taking-down Game Animals or Ending a Felonious Assault
Since we’ve debunked the myth of “kock-down power” above, we will focus on rapid incapacitation since this is the goal of both hunting and personal defense. In general terms, there are only two ways to incapacitate a game animal or a violent assailant. The first is instantaneous or rapid incapacitation via interrupting the central nervous system and the second is a more gradual incapacitation through severe blood loss. Since shot placement, wound dynamics, and numerous individual factors affect the end result, the two types will be covered separately in the following paragraphs.
Instant or Rapid Incapacitation: The only way to take down a game animal or felonious assailant instantaenously is to create a sufficient wound in a critical area such as the medulla oblongata area of the brain or in the upper spinal cord. The medulla oblongata is the area of the brain that controls bodily functions such as breathing and muslce movement. Similarly, the upper spinal cord connects the brain to the rest of the body and transfers information to the heart and other mucsles. A shot to this area immediately prevents the brain from controlling both breathing and all voluntary muscular movement, causing instant incapacitation that prevents the game animal from running away or the assailant from continuing an attack. Keep in mind, this is a very small area of the body: few game animals or assailants present unobstrutcted standing targets in ideal lighting, and few shooters have trained to a level in which they can fully manage stress and adrenaline to accurately place a well aimed shot in this area.
Gradual Incapacitation through Severe Blood Loss: Shots to any other area of the body can incapacitate, but only to various degrees which will depend on a combination of physiologial and psychological factors that span from seconds to hours. Regardless, both the game animal and the assailant can continue to run or fight until severe blood loss causes the blood pressure to drop to a level where circulation to the brain is lowered to the point of unconsciousness and eventual death. The FBI report explicitly states that “Failing a hit to the central nervous system, massive bleeding from holes in the heart or major blood vesels of the torso causing circulatory collapse is the only other way to force incapacitation upon an adversary, and this takes time. For example, there is sufficient oxygen within the brain to support full, voluntary action for 10-15 seconds after the heart has been destroyed.”
I’ll briefly cover the effects of projectile impact in different parts of the body.
- Areas of the brain outside of the Medulla Oblongata – different parts of the brain control vision, concentration, and both gross and fine motor skills. Terminal impact and destruction of these areas can affect the game or assailant in dramatically different ways. Blood loss, hemmoraging, swelling, and/or clotting can combine to accelerate incapacitation.
- Areas of the spinal cord below the brain stem and neck – in the most general terms, severing of the spinal cord induces instant paralysis to the body below the point of impact. Depending on where this severing takes place, one can assume that all areas above the point of impact can remain functional.
- The heart and central chest cavity – see the FBI note above.
- Major arteries – severing major arteries can rapidly lower the blood pressure to a point where circulation to the brain is diminished allowing for the onset of unconsciousness.
- Major weight bearing skeletal structure – a direct impact to the shoulders or hips of game animals or the pelvic girdle in human assailants can immediately limit mobility, prevent escape of the game animal, and limit an assailant’s movement. In the absence of severe blood loss, however, both the animal and assailant can remain vigilant and continue to flee or attack in a diminished capacity.
- Abdomen or other extremities – again, in the absence of severe blood loss, the animal can flee and the assailant can continue the attack for several minutes.
Aside from overwhelming destructive force or instantaneous incapacitation from a major wound to the Medulla Oblongata or upper spine, psychological factors can play a major role. These factors include shock, a mindset of rage or uncommon resilience, the presence of bodily produced drugs such as adrenaline, or the presence of narcotics can either amplify or abate the destructive effect of a projectile’s impact on the body. For every case study that illustrates an assilant’s ability to continue an attack even after receiving numerous life-threatening wounds, whether through rage or narcotics, there are roughly an equal number of accounts of defenders succumbing to non-life threatening wounds due to the rapid onset of shock.
So what role does pain play in terminal ballistic effect? The FBI notes that pain is irrelevant to survival since it can be suppressed through internal means such as focus, rage, and/or adrenaline or through introduction of narcotics. Again, returning to the point that there is no such thing as “knock-down” power, how is it possible that so many shooting victims “fall down” when shot? This is an interesting psychological factor that attributes this effect to popular media such as books, television shows, and movies. In general terms, civil society has been indirectly indoctrinated to fall down when shot.
While I’m not really a fan of viewing and sharing photos and videos of combat footage, I do want to share the short video below to explicitly demonstrate the difference between the human body’s response to a non-incapacitating shot and an incapacitating shot. In this video an Iraqi insurgent is preparing to fire an RPG when he is initially shot in the pelvic area. For a few seconds, he is sitting on the ground and appears to be regaining his bearing and planning his next move. The next volley of shots strike him in the upper neck and most likely in the Medulla Oblongata. At that very moment, he falls limp and unable to continue the attack. Warning, this video is graphic. If you prefer not to watch it, please continue to scroll down the page. <Graphic Content>
So far, we’ve introduced the key concepts to understanding Terminal Ballistics. Please check back with us for the next installment which will take a closer look at the terminal ballistic effect of different projectiles and conclude the Ballistics Series.