Firearms and Firearm Identification

Firearm Injuries

Firearm injuries occur when someone is shot by a bullet or projectile from a firearm. Injury varies and largely depends on anatomical location and ballistics. The mode of injury depends on the shape, velocity and possible deformation or fragmentation of the missile. Effect of the bullets on bone is dependent on bullet velocity. High-velocity bullets cause bone fragmentation and have the additional effects of cavitation and shock wave injury.

Gunshot wounds can be typical or atypical. The majority seen in practice are atypical, where it may not be clear what is the entry and exit wound.

Definition of terms

• The examination of firearm wounds allows for the determination of the following aspects of the injuries:
  • Range of fire: the muzzle-to-target distance – contact, near contact, intermediate and distant
  • Trajectory of the missile or projectile
  • Type and extent of the injuries inflicted by the projectile

Firearms

• Mechanism of firing a gun
  • Every firearm has a chamber where the catridge is lodged. The chamber leads to a hollow steel tube known as the barrel.
  • The spring is released on pulling the trigger
  • The proximal end of the chamber has a small hole where a pin move forward to strike the base of the cartridge. The striking action produces heat which ingnites the primer.
  • This initiates burning of the powder charge producing extremely hot and explosive gases which propel the bullet or pellets through the barrel and out of the gun
  • The bullet is propelled together with a jet of flame, gases, soot from the combustion, and burning and unburnt gun powder (gunshot residues). The detection of these materials on skin in or around the wound is essential to make a diagnosis of contact or intermediate gunshot wound

Classification of firearms

Firearm wounds

Definition of terms

• Factors that determine the severity of firearm wound
  • Mechanical interaction between the projectile and the tissue
  • Effects of the temporary cavity produced by the projectile
• Direct laceration of tissues
  • A drilling effect that occurs with any penetrating object. This is the main mechanism in low velocity gunshot wounds.
  • Seen in autopsy as a permanent cavity.
• Temporary cavity formation
  • This is produced by large amounts of kinetic energy being transferred to the tissue. It is primarily seen in high-velocity gunshot wounds.
  • If the pressure of the temporary cavity exceeds the elastic limit of the tissue the organ may be disrupted (”bursting effect”). Inelastic organs such as the liver are susceptible to this.
  • Seen in autopsy as a wide zone of hemorrhage that surrounds the small permanent cavity

Firearm Identification

This is done by ballistics, which can be used to identify:

• Type of bullet
• Type of firearm
• Serial number on the weapon
• Gunshot residue pattern on hands clothes or wounds
• Estimation of muzzle-to-target distances

Methods employed include:

1. Comparing of rifling marks: as a bullet is expelled through a barrel, the rifling causes it to spin leaving impressions on the bullet surface. These indentations can help to identify the firearm used as no two rifle barrels are alike.
2. Cartridge identification: cartridges fired from an automatic firearm show repetitive marks which are useful in the identification of the type of weapon used. Striated action marks imprinted on the cartridge include chamber marks, firing pin drag marks, shear marks and ejector marks.
3. Bullet and cartridge comparison: to match bullets to a gun, test bullets must be fired through a suspect firearm for comparison with the crime bullet. This is done using a comparison microscope
4. Firearm discharge residue (Gunshot Residue – GSR) identification
   1. Primer: lead, antimony and barium
   2. Powder: nitrocellulose, nitroglycerine
   3. Bullet: Lead, copper, iron
   4. Cartridge: copper, zinc, nickel
   5. Barrel: iron, oil

• Greiss test: a test carried out on or around bullet holes to pick up residues of unspent gunpowder. Nitrites are found in incompletely burned powder while nitrocellulose is found in modern smokeless powders. When the Greiss reagent is added to a nitrite-containing sample, it turns pink. The reagent may be sprayed on the hands of a suspect or on the body of the victim, and observed for the colour change

• Sodium rhodizonate test: detects lead residues
• Scanning electron microscopy with an energy dispersive X-ray analyser (SEM-EDX): specific for characteristics and morphological analysis of inorganic gunshot residue particles

Effects of projectiles on the body

1. When the missile penetrates the skin it mechanically thrusts aside the tissues along a track wider than the missile
2. The tissues are lacerated or crushed. Secondary damage occurs from the rupture of blood vessels and other structures resulting in a permanent wound cavity
3. High-velocity projectiles produce cavitation
4. Bullets may fragment or bone spicules from fractures may result and act as secondary projectiles to damage tissues
5. Pellets from shotguns are spherical balls of lead, that do not travel far, disperse easily and have poorer penetrating ability than bullets. The disadvantage- they are discharged en masse from the barrel and cause extensive damage

Gross examination and findings

• Examine all wounds carefully before cleaning the body, as well as the hands
• Photographs of a wound before and after cleaning should be taken for documentation of the findings
• Compare the wounds noted externally with the number of projectiles found in the body on radiographic examination
• If surgery has been performed, consider that a bullet may have been purposely or inadvertently removed during the procedure
• Localisation and measurement of wounds should be done. Use consistent reference points and anatomical landmarks.
  • The wound is generally measured in 2 dimensions and described by its shape
  • The presence or absence of any abrasion rim should be noted, as well as any soot or powder stippling. The extent of all these should be measured

Entry wounds

Skin wounds can help to determine the type of wound i.e., whether entry or exit. The skin is elastic and resilient, therefore gunshot perforations may be small and can easily be missed as a result of the initial perforation recoiling to a smaller puncture.

The distance between the muzzle end of the barrel and the target is called the range.

Range

Shotgun wounds

• A contact shotgun wound will resemble that of a single projectile, as the shot charge enters the body en masse
• As the muzzle-to-target distance increases, a more irregular entrance wound with scalloped edges may occur due to early pellet spread
• As the distance becomes a few metres, the margin of the wound will become rugged
• At a slightly longer distance, individual satellite defects may be seen around the main wound due to individual pellet strikes

Exit wounds

They are more irregular than entrance wounds. They are NOT associated with muzzle imprinting, searing, soot deposition or stippling. The edges are often torn, resulting in a stellate configuration or a rugged appearance. There may not be a central defect once the skin edges are approximated. They have no abrasion rim.

In the event of a low-velocity exit, they have a slit-like configuration which is deceptively sharp-appearing and can mimic a stab wound. Exit wounds are not always larger than entry wounds, and a protrusion of fat and viscera is not always a feature of all exit wounds (herniation may occur due to gravity or pressure).

• Differences between a typical entry and exit wound Entry wound Exit wound Margins Regular outline with a punched out appearance Irregular, jagged, erratic and lacerated Rim of abrasiion Usually has a rim of abrasion Usually no rim of abrasion unless the body was pressed against a surface Size Smaller, although in high velocity injuries it may be larger than the exit wound Larger Edges Inversion of the edges of the wound Eversion of the edges of the wound

Atypical wounds

Occur due to the instability of the bullet as it loses speed or passes through a first target first, or is obstructed by a door or a window. The wounds are usually irregular. Obstructions may also cause bullets to fragment, leading to the creation of secondary missiles which cause multiple punctate wounds referred to as ‘pseudo-tattooing’.

Microscopic examination and findings

Wounds may show crush of tissue with haemorrhage on histological examination. If the interval between injury and death is long, typical healing changes may be present. Soot and gunpowder grains may also be seen particularly in the case of contact wounds, which will also show superficial thermal alteration of the tissues.

Self-inflicted (suicidal) firearm wounds

• Suicide notes are found in a minority of such cases
• The weapon must always be present
• The range must be within arm’s length, depending on the nature of the weapon and excluding some mechanical device to fire the gun
• Sites of election include the temple, neck, mouth, and chest. Rarely do the patients shoot themselves in the eye or abdomen
• Suicidal wounds will either be contact or intermediate range
• Multiple firearm wound suicides are not common