Terminal Ballistics

The use of firearms in crimes has been rapidly increasing, and it seems that one cannot turn on the news without hearing that some crime had been committed with a firearm. Using ballistics as evidence is a way for law enforcement officers to help solve crimes and potentially capture criminals. Ballistics is a very complicated science, where every single detail matters. Every micro-measurement makes a difference when analyzing firearms and ballistics. The most complicated part when solving a crime involving firearms is the fact that no one can recreate the same exact shot. Even though it is an impossible task to do, experts can still duplicate scenarios and environments similar to the original crime, giving law enforcement more evidence to put

away criminals.
Ballistics is defined as the “science or study of the motion of projectiles, as bullets, shells, or bombs…the art of or science of designing projectiles for maximum flight performance” (dictionary.com). In forensics, ballistics is defined as “the area of Forensic Science that deals with firearms; how they are used, why they are used and why they are used frequently in the practice of murder” (Explore Forensics). This means that ballistics scientists can look at individual parts and pieces of a firearm or a bullet and it’s casing, to figure out aspects of the crime. The experts also have to deal with flight patterns, laws of gravity, speed of winds, atmospheric pressure, and every other natural science principle that can affect the flight patterns of a bullet. When at the crime scene, analysts collect certain evidence from the scene, such as “firearms, cartridge cases, bullets, live ammunition, trace materials, and any material damaged by a projectile” (Forensics Science Central). Even examining the wounds on a victim can help identify the type of firearm used, the range in which the bullet was fired from the gun, and the angle at which the victim was shot.
Firearms are separated into a few categories. There are handguns, rifles, and shotguns. Offgridsurvival.com gives a simple anatomy breakdown of handguns, rifles, and shotguns. The main parts of handguns include the bore, which houses the bullet when it is on it’s way out of the gun, the breech (chamber), where the cartridge is sitting when it is inserted, the grip, which is the place that a person holds the firearm, the hammer, which cocks back and hits the primer on the bullet, the trigger, which is pulled when a person wants to fire the gun, the trigger guard, which covers and protects the trigger, the magazine, which holds the bullets before they are inserted into the breech, the muzzle, where the bullet exits the firearm, the safety, which keeps the handgun from unwanted firing, and the sights, which help the person accurately shoot. Rifles and shotguns are similar in anatomy to handguns with a few different adjustments. The grip on the rifle or shotgun is called the stock. They also have an ejections port, where the cartridge is ejected from the chamber, and a longer barrel.
Ballistics is separated into three categories: internal, external, and terminal. Internal ballistics deals with everything that goes on inside of the firearm, in the timeframe of when the person pulls the trigger and when the bullet exits the firearm. External ballistics deals with the time when the bullet exits the muzzle and when it hits a target. Terminal ballistics deals with the impact of the bullet upon a target.
To better understand internal ballistics, one must be informed of what a bullet is composed of and how a gun works. A bullet is composed of “the primer, the propellant, and the bullet proper” (Explain That Stuff). The primer starts a controlled burn inside of the breach, and starts the process of moving the bullet out of the chamber. Next, the propellant is a “chemical explosive that powers the bullet through the air from the gun to the target” (Explain That Stuff). Finally, the tip of the bullet is called the bullet core, which is the part of the bullet that hits the target. The bullet core, propellant, and the primer are surrounded by metal, which is called the casing. The casing is the evidence that is left over when the gun fires and the bullet core hits the target. When someone pulls the trigger on the gun, the “spring mechanism hammers a metal firing pin into the back end of the bullet, igniting the small explosive charge in the primer. The primer then ignites the propellant—the main explosive that occupies about two thirds of a typical bullet's volume”(Explain That Stuff). After the propellant is ignited, it generates a lot of pressure because of the buildup of gas, then “The gas shoots from the back of the bullet, increasing the pressure behind it, and forcing it down the gun barrel at extremely high speed [300 m/s or 1000 ft/s is typical in a handgun]” (Explain that Stuff). The propellant does not ignite all at once. It slowly builds up, which causes the bullet to smoothly exit the muzzle of the gun, and “when the gas from the explosion shoots the bullet forwards with force, the whole gun jolts backwards with an equal force in the opposite direction [recoil]…the explosion that fires a bullet happens in the confined space of the gun barrel. As the bullet flies out of the gun, the pressure of the explosion is suddenly released. That's what makes a gun go BANG!” (Explain That Stuff).
External ballistics concentrates on the path the bullet takes, and the variables affecting the flight of the bullet. According to the Sierra Reloading Manual, “when a bullet flies through the air, two types of forces act on the bullet to determine the path [trajectory]…the first is gravitational force; the other is aerodynamics…the most important of these aerodynamic forces is drag…the drag force and the gravitational force together determine the trajectory of any spin-stabilized bullet” (1028). When analyzing bullet trajectories and paths, scientists must have a way to track the bullet itself. While there are many ways to track bullets, according to Sierra Reloading Manual, “the Doppler radar method is far and away the best method of measuring ballistic coefficients, mainly because it provides measurements of bullet performance throughout bullet flight from supersonic velocity levels through subsonic velocity levels” (1013). This is a reliable system because it “tracks the bullet as it flies and provides measurements of the radial velocity of the bullet with respect to the antennas; that is, with respect to the firing point” (1013). After it tracks the bullet, it downloads the findings, and processes them mathematically, and “the results of the computations are bullet position coordinates [downrange, crossrange,and vertical directions], bullet velocity components in these directions, and even drag deceleration, all versus the time of flight from the firing point” (1013). While the Doppler radar system is a viable asset to have when solving crimes, these systems are extremely expensive, and it requires a large computer and a group of experts to operate the machine and process the information, making it impossible for every department to have and control the machine.
Terminal ballistics deals with the bullet hitting the target, and the amount of damage the bullet itself causes.

“Terminal ballistics is in many cases, the least considered aspect of ballistics when determining the kind of bullet to use for a specific purpose…terminal ballistics is the study of how a projectile behaves when it hits its target and transfers its kinetic energy to the target. The bullet’s design, as well as its impact velocity, plays a huge role in how the energy is transferred” (Hornady). There are two ways that bullets can cause damage to humans and animals alike. “The primary way a bullet causes damage is through the permanent cavity it leaves - the hole that is created as the bullet passes through skin, bone or flesh. This wound channel is the same diameter as the bullet/bullet fragments and is a function of bullet penetration and expansion” (Hornady). The second way that a bullet causes damage is “by the temporary cavity it causes. When a bullet hits soft tissue, the tissue acts more like a fluid than a solid as it gives way and tries to absorb the bullet’s energy. The bullet does not immediately penetrate the tissue; instead it makes an impact crater that stretches in until the bullet penetrates the tissue” (Hornady). While the bullet continues stretching the tissue, the tissue is under so much pressure that it is ripped and torn while trying to assume it’s original position on the body. While studying terminal ballistics, experts must take into

consideration the bullet itself. “Bullets designed with heavier jackets tend to stay together better and penetrate deeper, while lighter jacketed bullets tend to fragment and expand more rapidly, creating a wider wound channel and increasing temporary cavitation, but generally don’t achieve as much penetration” (Hornby). The tips of the bullets are also important factors when investigating because “Expansion can be controlled by the bullet’s tip design and by the jacket construction. Rapidly expanding bullets create a wider wound channel, displacing even more tissue and increasing temporary cavitation, but they also increase drag, thus requiring more energy and momentum to drive through tissue, and in general don’t penetrate as deeply as bullets designed to expand more slowly” (Hornby).
Ballistics evidence is important in court cases because “much of its evidence is used in criminal proceedings…the use of ballistics research can prove a link between many different crimes carried out over a lengthy period of time” (Explore Forensics).

Even if there wasn’t a firearm collected at the scene of the crime, “Firearms examiners…can provide a list of possible firearms that may have fired the projectile…The fact that the lab can supply a list of manufacturers whose barrels match the twist rate and direction of the fired projectile is significant. In cases where the gun isn't immediately recovered, investigators can limit their search to only certain firearm brands” (Spraggs). When regarding firearms examiners, it is important to remember that examiners cannot establish who committed the crime, and when the crime took place. The only way that forensic scientists can figure out who committed the crime from the gun itself is through DNA evidence or the gun registration (if any).

Ballistic examiners have an important place on the witness stand, if they are subpoenaed to testify during a trial. Because only expert witnesses can give their opinions on trial matters, defense and prosecuting attorneys must call experts to give their testimony. Ballistic scientists are considered to be expert witnesses, and they can form their own professional opinions on what they fid during their tests. The evidence that they acquire can make a huge difference in the case, and can sway a

jury to decide their verdict.
Ballistics is important evidence when solving firearms-related crimes. It is a very complicated science, and it is difficult to find and prove as evidence because it is impossible to recreate the exact shot that was taken, under the same exact conditions. However, new technologies are making ballistics more reliable, and more likely to hold up in court as evidence. Forensic ballistics is becoming more and more reliable, and is considered to be one of the more important aspects of forensics when solving crimes. From identifying weapons, to discovering trajectories, the evidence that ballistics provides is vital to solving crimes.