Clay Chastain - 1 -
Clay Chastain
ANTH – Forensics Seminar
Dr.Hamilton
6 May 2007
Ballistics Trauma to the Cranium: An Introduction
While many fields of forensic anthropology exist today, one of the more applicable areas of study is that of ballistics trauma, especially to the cranium. As commonly known, projectile weaponry, or guns, is a major source of death throughout the world; in North America alone, firearm deaths are not uncommon and constitute a considerable amount of forensic cases. Because of this, understanding the basic principles involved in the forensic role of ballistics and their features allows forensic anthropologists to correctly identify and understand the elements of ballistic trauma. While most forensic anthropologists probably have a wide range of understanding on this subject, the amount of information relating to gunshot wounds to the head is quite ample in certain situations. Despite this, there is a significant degree of information which may help to reinforce or refresh some underlying ideas involved with ballistics trauma and its effect on the skull.
However, before delving into the complexities of cranial trauma via gunshot, it is advisable to explain the nature of many forensic cases. Even with a set of standardized information, determining exact features of trauma or the instrument that caused it may be strikingly difficult due to the high chance of variance from person to person. That is, average results will serve well to explain the average situation, but many situations call for unique investigation due to a number of factors (essentially, every death is different). Additional elements can include everything from the working condition of a gun (which can affect velocity severely) and defects in everything ranging from the victim’s skull to that of the actual bullet. This said, this information will still serve as a solid introduction to ballistics trauma, but every case will inevitably be different. Because of this, a variety of topics that effect gunshot trauma will be discussed along with the actual effects.
The first and foremost topic that should be explained is just what ballistics actually is. Di Maio, as well as many dictionaries, defines ballistics as “the science or study of the motion of projectiles, as bullets, shells, or bombs.” However, for the purposes of sticking to common lethal instances in domestic life, bullets and shells will be the primary focus. In a military context, the study of projectile explosives (such as RPGs, or rocket propelled grenades) is a valid interest, but it is not an ordinary situation in North America. Surprisingly, this field also incorporates low velocity projectiles as well, such as BB’s or pellets, a situation which in rare cases can produce death. Yet again, for the purposes of this, the focus will be laid upon higher velocity weapons.
Following this, high velocity weapons are generally broken down into several groups (generally three tofive [some groupings include machineguns or submachine guns]). First on the list are the handguns, which have very small caliber (or diameter) ammunition, and they feature a relatively low velocity as well. Handguns are currently the most purchased personal defense weapons in the United States, meaning that this section is often quite applicable to forensic cases. However, the other two types of weapons also have a large purchase rate (assumedly for hunting purposes, although this is speculation). The second type is the rifle, which is a large caliber weapon. These weapons have a higher accuracy over longer distances, largely due to their projectile velocity. The third type is the shotgun which fires small circular balls at relatively low velocities.
Further investigating these types, there are a large variety of subgroups among these three major groups. For handguns, there are about four basic types. The first of which is a single-shot pistol; these pistols, as the name suggests, carry only a single round and must be reloaded after each shot. These are generally purchased for self-defensive or for hunting purposes. The second type is the derringer, which is a variant of the single-shot pistol; derringers are very small, compact guns that are easily concealed and often used as a last resort defensive method.Traditionally, derringers have two single-shot barrels that are loaded independently from one another.The third type is the revolver, which is the most purchased form of handgun in the United States today because of its low price and dependability; just as it sounds, this pistol uses a revolving chamber to hold a standard of six bullets. The last group is the auto-loading pistols, more commonly referred to as automatics (or just as pistols because of the confusion that “automatic” often generates); these pistols featured a magazine-fed clip that inserts a new cartridge after the previous one has been spent.Generally the magazine is placed in the grip of pistols, however, some guns such as the Tec 9 have the magazine in front of the trigger guard – but this is more of an aesthetic implementation that anything else. After this point, there are literally dozens of different handguns with different designs which each may affect ballistics trauma in a unique way.
For rifles, there are two main groups: the rifle and the automatic rifle (or assault rifle). The rifle is a firearm with a rifled barrel which is designed to be fired from the shoulder; there are many different types of rifle, including the single-shot, lever-action, bolt-action, pump-action, and auto-loading (or semi-automatic). However, the basic principle of the rifle stays the same throughout these changes. Some of the more common rifles include the bolt-action rifle (which was used during much of World War I and II, especially with the German-made Kar98 rifle) and the semi-automatic (not to be confused with a fully automatic rifle). The second grouping of the rifle is that of the assault rifle, a weapon which must meet the following criteria: auto-loading, has a large-capacity (of 20 rounds or more) detachable magazine, is capable of fully-automatic fire, and fires an intermediate rifle cartridge. These weapons are not to be confused with “assault pistols”, which are generally cheaply made guns that are purchased by uninformed buyers. An example of an assault rifle would be the M-16 or the AK-47, common military weapons used throughout the world. Di Magio notes that deaths by these weapons in North America are very rare, largely because of their high price, large size, and the large amount knowledge needed for operation.
For shotguns, there are many types as well, all of which must have an 18 inch barrel to be considered legal. Some types include the single-shot, the over-and-under (a vertical barrel setup), the double-barrel, bolt-action, lever-action, pump-action, and auto-loading. Common types are usually the single shot because of their cheap price and ease of use.
Next, each type of firearm mentioned above uses a very specific ammunition which will affect the skull differently upon impact. For handguns, the round nose and the hollow-point bullet are some of the most common purchases for ammunition, but other choices include the wadcutter or the semi-wadcutter. The round nose bullet is just as it sounds, a bullet with a more rounded shape. This is the stereotypical 9mm ammunition that most handguns use. However, the hollow-point is a bullet designed to increase mushrooming, or mushroom-shaped deformations in flesh (and consequently affecting entry and exit wound sizes). These bullets were created for the intent of having more killing power by increasing deformation instead of the clean entry of the round nosed bullet. The wadcutter and semi-wadcutters are specially designed bullets which are often used in target practice and not often seen in cases of homicide.The caliber of a typical handgun bullet is on a range from .22 to .45, with .45 being larger than .22. As mentioned, handguns have relatively little firing velocity. Even a Magnum, one of the most powerful handguns only have a velocity of a very low end rifle; that said, the approximate distance of which the Magnum is fired can make it far more powerful when impacting the skull.
Before progressing more, it is essential that some more of the bullet is broken down. Many bullets have jackets, which are metal coatings designed to impact both flight dynamics and deformation. Generally, a bullet is composed of primarily lead with a mixture of other elements to stability and form; however, a jacket is often applied to a bullet, such as one made of copper. These help decrease bullet deformation and increase penetration ability. They also improve high velocity stability. Because of this, a large number of assault rifle bullets are completely jacketed. That said, even regular handgun bullets are jacketed or semi-jacketed for the same reason.
In rifles, the ammunition is an elongated bullet with a more pointed tip. This design is used to increasing the length of flight at a high velocity (increasing shot range). Many of these bullets are, as mentioned, fully jacketed. Some even have aluminum tips which compact upon impact, creating more impact force through dense surfaces, such as body armor. But because the head is not covered with Kevlar in a typical situation, this bullet will have a similar effect of a regular rifle round with a jacketed coating. A note regarding this ammunition is that the velocity in these rounds is high enough to enter and exit the head without much bullet deformation, creating a clean wound. However, up close, the results in a fleshed wound can look strikingly similar to that of a shotgun.
That said, a shotgun is a completely different sort of ammunition. This weapon fires multiple projectiles in a shell. The major divisions include buckshot, a ball intended for deer, and birdshot, a ball intended for birds. Logically, the birdshot is much smaller than that of the buckshot – shooting a bird with buckshot would lead to the bird being blown apart. A shotgun fires these pellets with relatively low velocity but this is made up for by the randomization of the shot, creating multiple wounds on a subject. Often when hitting the head, a ball with penetrate the skull but not exit; instead, it will ricochet around instead the skull, causing more trauma to the fleshy matter of the brain, and a few pock marks where the pellet happened to bounce. Most commonly, a pellet will enter in a straight line, hit the opposite side of the skull, and roll around on the outside of the brain. However, with enough velocity, it will hit and bounce at about a 25 degree angle through the middle of the brain.
An interesting note on ballistics is the surprisingly large number of different types of ammunition. Some ammunition is specifically designed to penetrate, while others are aimed at causing the most damage. For example, exploding ammo was used to shoot Ronald Reagan in his assassination attempt; this ammo breaks apart as it impacts, creating massive internal trauma. Soon after this, the ammo was made illegal to purchase. Other commercially available ammunition includes mushrooming ammunition which uses a very easily deformable metal that blows out around a pointed tip, ripping a large hole in fleshy matter. Because of this variety, it is reasonable to think that not only the flesh, but also the skull itself will receive different trauma based on a number of factors.
The first step of a bullet penetrating into a bone is beveling. Literally, upon impact, a portion of the bone is chipped away. Due to the velocity, this often happens at the opposite side of the impact. For instance, if a frontal bone is shot, there may only be a small circular hole showing the impact. However, from inside the skull, the exit side of the entry wound can have a massive amount of bone damage (an inward bevel). The bone is blasted into small chips which, unfortunately, also act as projectiles, damaging the brain along with the bullet itself.The area which is chipped out is rounded and is sloped, much like a volcano shape inverted.The exit wound, if any, often has similar beveling (a outward bevel). Much of the beveling is, frustratingly, variable, depending on the situation, creating cases of reverse beveling where the opposite of the expected is caused. This can happen from a number of sources, but this is usually based on the gun used, the distance it was fired from, where it impacted, and the type of ammunition used. Due to this, it creates a large variety of possibility for every incident. Regardless, the typical situation (often found with 9mm ammo that is jacketed or semi-jacketed) is one where the entry wound is inward the exit wound is outward. Also of mention, some exit wounds may not be beveled to any real degree because they were irregularly ejected from the skull, which will be mentioned later.
Not all bullet wounds to the skull are round holes because of a number of factors. As can be imagined, velocity and the type of ammunition may affect both the entry and exit wound, along with any number of extra conditions. In general, entry wounds are usually round, oval, or keyhole in shape; however, it is possible to have an irregular entry as well, due to previous ricocheting which deforms the bullet prior to entry, or from shots which have so much force that the bone is pulverized into very small particles. The oval and keyhole shapes can happen for a variety of reasons, one of which being the angle at which the projectile hit. A higher velocity pistol shot generally creates a round entry hole, for example, whereas a shotgun would produce an irregular entry wound, especially at close range. Oval wounds often come from incomplete or odd-angled shots. Keyhole wounds also come from odd-angled shots which end up chipping away the bone before they enter the skull. Exit wounds are a completely different story. Depending upon the type of bullet, velocity of impact, and the point of impact, the exit wound may be completely irregular. Because bullets are made of lead, the amount of deformation to the metal may be great, even leaving pieces of the metal separated from the core. When the force is present to create an exit wound, the bullet may have been deformed to such a degree that it impacts awkwardly, leaving a large hole of shattered bone in no particular shape (although there is a relationship to deformation, its rotation, and exit hole sizes). In regular entry and exit wounds, the size of the caliber is in a direct relationship to the size of the hole.
The next feature of ballistics trauma is that of fracturing. There are three general types of fracturing: radiating, concentric, and butterfly. For this context, the butterfly fracture occurs on long bones, which is not applicable to cranial trauma. Radiating fractures, however, occur when the stress from a bullet impacts transitions force toward an area of greatest weakness. That is, a fracture will form radiating away from the bullet hole to a weak point, such as a suture. By doing this, it relieves all of the stress which has accumulated from the wound. From this point, the remaining stress is distributed evenly around the weakness. However, on shots with extreme velocity, a concentric fracture may occur. This happens when the stress put on the skull is so great that it “ripples” back through the skull, creating circular fracture rings.Rifles and assault rifles often meet the criteria needed to produce this type of fracture. Lastly, another group of fractures may occur which are irregular. These fractures come from excess stress (secondary fracturing) or which otherwise cannot be determined, such as the effect of when buckshot hits multiple areas at a very similar time. As well, all of the fractures could theoretically be present on a skull.The variables which often affect the formation of the fractures include the configuration of the bone, the bone density, and suture location.The general method for dating when a fracture occurred is to look at the shot that is believed to be first – its fracture lines will be complete, hitting a weakness before dissipating. The next fracture will instead hit the weakness caused by the initial fracture, a fracture line. In this way, it is possible to trace which shots came first. Unfortunately, in the case of extreme cranial trauma, it may be very difficult or impossible to put an estimation of the series of shots.
Another initial complication to ballistics trauma is that on fleshed wounds, it may be very difficult to determine how the wound was caused. For example, a rifle wound to the head can create massive damage, similar to that of a shotgun blast. It would take a degree of investigation (finding buckshot at the scene, or being able to identify clearly multiple entry wounds). Otherwise, the skull would otherwise have to be reconstructed (which is a standard practice in forensics cases).In a case where the bone was pulverized due to a high velocity shot, it may be impossible to narrow down the type of ammunition past a rifle-based form; even at this stage, it would take a degree of effort to affirm the actual type of weapon used. Again, this can lead to complications positively identifying the gun which created the wound. Thankfully, in many situations, the bullet is still present either in the skull or nearby; if anything, the casing may have also been left. Further, the presence of powder used in the firing of the gun may be helpful in determining more exact specifications. Another saving grace on fleshed wounds is the presence of powder burns, which often leave predictable, patterned marks.