Firearm Wounds and Ballistics Quiz

Firearm Injuries

• Firearms are weapons designed to propel a projectile through the expansion of gases generated by the combustion of an explosive substance.
• Rifled weapons have spiral grooves in the barrel, with lands between them.
• Lands bite into the bullet as it travels through the barrel, causing it to spin.
• The number of lands and grooves (primary rifle marks) are unique to each weapon, thus identifying the specific firearm.
• Caliber is the bore diameter, expressed in hundredths of an inch or millimeters, measuring the distance between two opposite lands.
• Rifled weapons can be long-barreled (e.g., service rifles) or short-barreled (e.g., revolvers, pistols).
• Non-rifled weapons (e.g., shotguns) have smooth bores and fire multiple projectiles (pellets).
• Mechanisms for firing involve: triggering the primer, igniting the explosive powder, the resultant gases pushing out the bullet, and the other projectiles and accompanying materials (i.e., wads, flame, smoke).

Wound Characteristics

• Firearm wounds exhibit tissue damage, cavities (loss of substance), inlet, exit, and a tract traversing between them.
• Externally, powder residue marks, and gunshot residue, may occur.
• Bullet or projectiles may be present within the tract.
• Bevelling may be observed in bones.

Mechanisms of Firing Rifled Weapons

• Primers are capsules containing mercury fulminate.
• Pulling the trigger activates the firing pin.
• The impact of the firing pin ignites the primer.
• The primer's fire ignites the gunpowder charge.
• Gas generated by the gunpowder combustion propels the bullet out of the barrel.

Gunpowder Types

• Black powder comprises C, S, and KNO3.
• Smokeless powder (modern type) uses nitroglycerine/nitrocellulose (single or double base).
• Primers contain lead azide, lead styphnate, mercury fulminate, lead thiocyanate, and antimony sulphide.

Effects of Gunfire in Rifled Weapons

• Gases, flames, smoke, and gunpowder and metallic fragments cause changes on the skin and/or material.
• Gas leads to wound edge eversion and cruciate lesions.
• Flame creates burning.
• Smoke leaves markings/smudges, especially apparent with black powder.
• Powder residue is deposited in the dermis and epidermis. Known as tattooing or stippling.
• Bullet penetration causes tearing and damage.

Angle and Direction of Firing

• Perpendicular firing creates circular inlets; angled firing creates oval inlets with abrasion on the side of impact closest to the gun; Grazing doesn't penetrate the skin completely, often producing elongated oval shapes..
• Gutter wounds develop if the bullet deflects internally, producing a track on the skin only.

Special Forms of Firearm Wounds

• Multiple exits suggest fragmentation of the bullet.
• Ricochet bullets may mark the object struck before entering the body.
• Irregular wound patterns suggest the bullet's tumbling or deformation during flight.

Non-Rifled Firearm Mechanisms

• Non-rifled weapons, especially shotguns, use shot (pellets).
• The mechanism of firing involves the firing pin activating the primer; igniting the gunpowder.
• The pressure of the expanding gas propels the wad forward (with any projectiles—pellets), and associated material, (i.e., pellets, wads, flame, smoke, unburned gunpowder) out of the shell (towards the target).

Range of Firing in Non-rifled Weapons (Shotguns)

• Contact wounds exhibit soot, muzzle marks, and possibly skin laceration.
• In the short range 0-15cm - a single circular wound; if the weapon is held at an angle—appears elliptical; hair singeing; burning and scarring; pink discoloration of the tissues within and around the wound; wads or plastic cups remain present—indicating the near distance.
• Intermediate or close range (up to 2m): - wound markings show scattering of powder stippling; often presenting perforated or scattered wound characteristics. (Individual projectile holes)
• Distant Range wounds (more than 2 meters): - less powder tattooing; holes of the caliber of the projectile; little to no burning or scarring; spread of the pellets is significant; the main wound hole diminishes as the distance increases.
• more than 4 meters (maximum): only individual projectile (pellets) holes; absence of a central hole; 'full dispersion' patterns are evident.

Effects of Gunfire on Non-rifled Weapons

• The effects of gases, flame, smoke and unburned gunpowder on victims is similar to rifle wounds, but occurs at differing distances.
• Effects of pellets and wads (non-metal items in shotgun shells), differ based on distance from the target.

Wads and their Identification

• Wads (felt or cardboard) from shotgun shells are often present in the first few meters.
• Wads may be retrieved during autopsy to determine the type of ammunition.
• Beyond the first few meters, wads are likely to fall to ground or otherwise be displaced from the target.

Choking Effect / Barrel

• "Choking" refers to a shotgun's narrowed barrel at the muzzle end.
• Choking reduces the spread of pellets.
• Choking effect varies with the type of shotgun and barrel.

Range of Fire Estimation (Precision)

• Careful comparison of the subject's wound patterns against test firing on similar material yields the most relevant findings.

Exit Wounds

• Typically larger than entrance wounds due to bullet expansion or tumbling as it exits the body.
• Lack gunshot residues.
• Bullet paths can be deflected by bones or dense tissues causing a non-linear exit wound and one that does not directly oppose an entrance wound.

Inlet/Exit Wound Differences

• Inlets usually show more extensive tissue damage than their corresponding exits..
• The shape of the inlet can be different from the exit wound, often being inverted or irregular, depending upon the angle of impact.
• Presence of gunshot residue is absent at the exit. (Whereas residue may be present at the area of the inlet).
• Tissue bevelling (at inlets) that occur in the areas of bone, will not exist to the same extent at the exit. The exit wound may only partially penetrate the target tissue.

Bevelling of Bone

• Bullet impact on bone causes displacement of bone fragments, and external beveling.
• The entrance is characterized by a smaller wound on the inner bone table and larger on the exterior bone table.
• The presence of external bone beveling is one important characteristic useful in assessing the trajectory of projectiles.

Complications of Firearm Injuries

• Contact/near-range firing often causes rapid death.
• Missile impact on brain tissue, neck injuries, chest injuries, abdominal injuries can cause immediate or delayed death.
• Long-bone fractures may cause fat embolism, and/or prolonged immobilization may result in pulmonary embolism.

Investigation for Firearm Injuries

• Objectives of investigation include determining if the cause of death or injury is due to firearms.
• Determining if the wound is an entrance or exit.
• Identifying the type of weapon (rifled or non-rifled) and the range of firing.
• Circumstances surrounding the injury.
• Cause(s) of death.
• Causative weapon identification.

Firearm Residue on Victims

• Visible residue like blackening, grease, and tattooing to materials (skin, clothes) are present—related to primer, powder, metal, and bullet.
• Other components like lead, barium, and antimony are also present, usually found from the powder or primer residues.
• Firearm residue may be found on the skin or clothing of the shooter, the victim, or on other target materials at the scene of injury. (e.g., Clothing, Hair, etc).

X-Ray Analysis

• X-Ray is useful for locating bullets/pellets/fragments.
• Assessing trajectory of firing based on bone/tissue damage/defects within the target of the injury.