| Introduction |
In order to properly assess gunshot wounds, it is necessary to have an understanding of the weapons and ammunition that commonly are used. This information will greatly assist an investigator with analyzing the characteristics of inflicted wounds and collecting relevant information and evidence at the time of necropsy.
For example, hunting seasons for certain species are structured as to allow hunting with specific weapons exclusively, e.g. bow and arrow, muzzleloader, or rifle seasons for white-tailed deer. By collecting the appropriate evidence during necropsy, the investigator potentially can match a weapon to the accused, prove that a fatal wound was inflicted by a specific weapon or type of weapon, and prove off-season weapon violations.
Another major issue with wildlife forensics cases in North America is the use of outlawed lead shotgun pellets. This type of ammunition was outlawed to help prevent environmental contamination with spent lead shot and the accidental lead poisoning of birds by ingestion and nonlethal wounding. Knowledge of the different types of ammunition available is critical to assessing such cases. |
| General Information |
Not everyone has had exposure to firearms, so we will give a few of the basics here and the relevance of different topics to wildlife forensics. Let us start with some simple definitions that come up in discussions about firearms. |
| Handgun – Firearm designed to be fired from the hand; pistol. Anyone that reads the paper or watches the news is familiar with these weapons. Cases of handgun wounds are more common in human crime; however, cases involving animals may be presented, especially when a handgun is used to inflict the fatal or “final” wound. |
| Long gun – General term that includes both rifles and shotguns. These comprise the majority of weapons in wildlife forensic cases. |
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| Rifle – The basic components of modern rifles include the barrel, magazine, loading and ejecting apparatus, and stock. The stock is rested against the shoulder to bear the force of the recoil when the weapon is discharged. The magazine is the location where ammunition is stored and fed into the loading and ejection port. Several different loading and ejection mechanisms exist, including bolt action, lever action, automatic loading. Modern rifles fire bullets that are loaded into cartridges. |
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| Shotgun – As with rifles, shotguns are constructed with the same basic four components. Shotguns are capable of firing pellets, larger metal balls (shot), or slugs. These projectiles are loaded into shells that contain propellant (gunpowder) and other components required for discharge, as discussed below. |
| Caliber – In the English measure, the size of a weapon is measured by the size of its bullets in hundredths of an inch. This system is used to classify most firearms, with the exception of shotguns. For example, a 38 caliber weapon fires a bullet that is 0.38 inches in diameter. The European system, of course, uses metric measurements. A weapon with a European measure that is familiar to most people is the 9 millimeter handgun. |
| Gauge - Shotguns are classified by an entirely different measure known as gauge. Gauge is measured by the number of lead balls with the same diameter as the barrel of the weapon that would be required to equal one pound. The most commonly encountered weapons are the 20, 16, 12, and 10 gauge shotguns. The larger the gauge, the smaller the bore of the weapon. The exception to this is the 410 shotgun, a smaller weapon that is a direct bore measure. |
| Smooth-bore firearm – Some shotguns and muzzleloaders do not have rifling grooves cut into their barrels. Thus, shotgun pellets, slugs, and muzzleloader balls fired from the weapons cannot be matched back to a specific weapon. The size of the ammunition used can be identified and potentially matched to the caliber weapon and ammunition in the possession of the accused. |
| Rifling – Grooves are cut into the barrels of rifles and some shotguns to place a spiral motion on a projectile as it leaves the barrel. This promotes a more linear flight path and is a similar principle to the spiral motion applied when throwing a football. Rifling marks left on a projectile can help in matching a projectile to a specific weapon. |
| Muzzle velocity – The speed at which a projectile leaves the barrel of a weapon. Muzzle speed usually is given in feet per second. |
| High velocity firearm – These weapons include most of the popular hunting rifles and have a muzzle velocity of greater than 2,200 feet per second. |
| Low velocity firearm – Shotguns and muzzleloader weapons fire heavier, slower projectiles with a muzzle velocity of around 1,300 feet per second or less. |
Components of a Cartridge |
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| Bullet – For the purpose of discussion here, a bullet will be defined as the projectile that is loaded into a cartridge and fired from a firearm. Bullets are available in various shapes, e.g., hollow point, and weights (measured in grains). See the cartridge diagram above. |
| Cartridge –This is a self-contained unit that includes an outer casing, projectile (bullet), propellant (gunpowder), and primer (source of ignition). Only the projectile is fired from the gun. The remainder of the spent cartridge is ejected from the weapon. |
| Cartridge casing – This component of the cartridge is usually composed of brass and can be vital in linking a weapon to a specific case. The cartridge ejection mechanisms of rifles leave characteristic marks that are analogous to the human fingerprint. |
| Jacket – The metal covering over a bullet that overlies a core of different consistency. Jackets are used to manipulate the degree of deformation that occurs upon impact. |
| Components of a Shotgun Shell |
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| Shotgun pellets – Shotgun pellets vary in size from 1.27 mm birdshot to 9.14 mm buckshot. The large diameter pellets are used to hunt larger game such as deer. Shotgun pellets may be made from lead, steel, and various alloys. As mentioned above, lead birdshot has been declared illegal in waterfowl hunting. |
| Shot cup – A shot cup is a plastic sleeve that is loaded into a shotgun shell prior to the projectiles. The cup holds the projectiles and facilitates their uniform discharge from the barrel. The shot cup falls away when a shell is discharged. Cup sizes are specific for different gauge shells. |
| Wadding – Wadding is the material placed between the propellant and the projectile. It is used in shotgun shells and muzzleloader-type firearms to distribute force on the projectile. Today, the wadding and shot cup usually is formed into a single unit. |
| Shot string – As pellets are discharged from a shotgun, they spread out over distance. The area covered by the pellets varies according to distance from the target and what is referred to as the choke. The pattern of the pellets as they reach a target is referred to a shot string. An animal’s location within the shot string will determine the number of pellets that strike it. |
| Choke - This term refers to the constriction at the end of the shotgun barrel. The extent of the choke affects the spread of the pellets following discharge from the barrel, thus manipulating the shot string. |
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| Slug – Slugs are another type of projectile that may be loaded into shotgun shells. There are two basic types, the Foster (right) and Sabot slugs (left). Foster slugs are grooved so that they rifle when fired through a smooth-bore shotgun. Sabot slugs are discharged with a polyurethane sleeve. Slugs primarily are used to hunt bigger game. |
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This is what the components may look like after discharge and collision with a target. |
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Note how the bullet mushrooms in impact. This will have relevance when we discuss entrance and exit wounds. |
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| Muzzleloader – These are old-fashioned single shot firearms that are loaded through the distal end of the barrel. With traditional muzzleloaders, each component, gunpowder, wadding, projectile, patch, is loaded separately and placed down the barrel by a ram rod (seen mounted below the barrel). The process must be repeated with each single shot. Modern muzzleloaders are available that lend to quick loading and impressive accuracy. Believed by many to be more “sporting,” many states have hunting seasons open exclusively to hunters using muzzleloaders. |
| Now that we have some of the basics covered, let's look at techniques used in evidence collection during necropsy. |
| Examining Gunshot Wounds >> |
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Veterinary Forensic Pathology | Guns & Ammo