Comprehensive Notes on Ballistic Injuries

Ballistic Injuries

Introduction

• The unlawful use of firearms continues to increase, with firearms being relatively easy to obtain regardless of jurisdictional controls.
• Legislation aimed at reducing firearm availability often impacts law-abiding citizens more than criminals.
• Forensic practitioners encounter injuries and deaths from various firearms, with firearm control being a point of political debate.
• Firearm injuries can be deliberate (conflict, assault) or accidental (hunting).

Types of Firearms

• Definition (England & Wales, Firearms Act 1968, section 57 (1)): A firearm is 'a lethal barreled weapon of any description from which any shot, bullet or other missile can be discharged'.
  • Includes prohibited weapons (section 5 Firearms Act 1968).
  • Includes any component part of a lethal or prohibited weapon.
  • Includes accessories designed to diminish noise or flash.
• 'Lethality' is complex and determined by the court (Moore v Gooderham [1960] 3 All E.R. 575).
• Two main types:
  • Smooth-bore barrels: fire pellets or shot.
  • Rifled barrels: fire single projectiles or bullets.
• Both types use detonation of a solid propellant to generate gases for propulsion. Airguns and air rifles use compressed gas.
• Unusual firearms: rubber bullets, stud guns (power-actuated/nail guns), humane killers.
• Modern propellants: nitrocellulose or synthetic compounds in flakes, discs, or balls.
• Firing sequence:
  1. Firing pin strikes the primer cup, causing the primer compound to explode.
  2. Flame spreads to the propellant through vents.
  3. Propellant rapidly burns, producing gas.
  4. Gas pressure propels the bullet or shot from the barrel.
• Muzzle velocity:
  • Shotguns: a few hundred meters per second.
  • High-velocity military weapons: 1000+ meters per second.
• Kinetic energy calculation: $\frac{1}{2}MV^2$ (where $M$ is mass and $V$ is velocity).
• Higher muzzle velocities are more effective at delivering energy, which is related to the extent of injury.

Shotguns

• Commonly used in sports, hunting, and farming.
• Long-barrelled, smooth-bore firearms that discharge cartridges containing shot.
• Single or double barrels (26-30 inches, or 66-76 cm).
• Double-barrelled weapons: side-by-side or over-and-under.
• Shortening the barrel has little impact on effectiveness at short to middle distances.
• Effective range: about 30-50 m.
• Cartridge structure (Figure 9.1):
  • Metal base (head) with central primer cap.
  • Cardboard or plastic tube containing propellant charge and shot.
  • Thin disc or crimp at the end of the tube.
  • Plastic wad or felt, cork, or cardboard discs (wads) above and below the shot.
  • Plastic wads open into a petal shape in flight and can contribute to injury at close range.
• Cartridge designation: based on shot size (typically 6-850 shot in a 12-bore cartridge).
• Some cartridges contain a single heavy projectile ('slug').
• Wound type depends on calibre, shot size, and distance.

Rifled Firearms

• Fire one bullet at a time through a barrel with spiral grooves (lands) that impart gyroscopic spin for a stable trajectory.
• Two main groups: hand guns and rifles.

Hand Guns

• Revolvers: contain a rotating cylinder for manual cartridge loading.
• Pistols (semi-automatic hand guns): contain a magazine within the grip.
• Discharge: firing pin or striker impacts the primer cup.
• Difference: method of operation (Figure 9.2).
• Revolver operation:
  • Cylinder rotates to align a new cartridge.
  • Double action: pulling the trigger.
  • Single action: manually cocking the hammer, then pulling the trigger.
  • Fired cartridge cases remain in the gun until manually unloaded.
• Pistol operation:
  • Forces from discharge recycle the weapon: extracting/ejecting the fired cartridge, resetting the firing mechanism, and loading a new cartridge from the magazine.
  • Semi-automatic: this occurs each time the trigger is pulled.

Rifles

• Long-barrelled weapons for accurate projectile firing at greater distances than revolvers or pistols.
• Various operating mechanisms: single-shot bolt-action to fully automatic gas-operated assault rifles firing >700 cartridges per minute.
• Cartridges (Figure 9.3):
  • Metal cartridge case (brass, steel, or aluminum).
  • Primer cup in the base.
  • Propellant within the case.
  • Single bullet fitted into the mouth of the case.
• Size and design depend on the weapon and desired ballistic performance.
• Rifle cartridges: larger case-to-bullet ratio for a larger propellant load, required for effectiveness up to 2 km.
• Bullet size (calibre) and design affect ballistic performance and kinetic energy transfer on impact.
• Wound formation is related to the transfer of energy to body tissues.
• Expanding bullets (Dum-Dum bullets): designed to expand on impact, increasing diameter to limit penetration or produce larger wounds.
  • Hollow-point and soft-point bullets are typical designs.
  • The Hague Convention of 1899, Declaration III prohibits the use of expanding bullets in international warfare.

Firearms Injuries

• Injuries originate from smoke, flame, and gases of combustion and the projectile(s).
• Unburned, burning, and burnt propellant, wadding, and plastic containers also exit the barrel.
• These items usually follow and may also precede the projectile(s).
• Travel distance depends on the weapon and propellant type.
• Particles can escape from gaps around the breech and soil hands or clothing.
• Presence and distribution of items and particles have evidential value.

Injuries from Smooth-Bore Guns

• Discharge forces pellets along the barrel using detonation gases.
• Pellets leave the muzzle in a compact mass, spreading out as it travels.
• Shot pattern expands as a long, shallow cone with its apex near the muzzle.
• Pellet spread increases with distance, increasing the area of potential damage (Figure 9.4).
• Forensic investigation: evidence assists with incident reconstruction, projectile trajectory, and range-of-fire.
• Comparison of marks on recovered bullets and cartridges with those from a suspect firearm.
• Firearms database links scenes and establishes gun crime trends.
• Specialist equipment determines projectile velocity and kinetic energy to establish ballistic performance and lethality.
• Used in the UK to assess the lethal potential of air weapons.

Contact Wounds

• Gun muzzle abuts the skin, resulting in a circular entrance wound approximating the muzzle size (Figures 9.5 and 9.6).
• The wound edge is regular with a clean-cut appearance and no individual pellet marks.
• Smoke soiling is present on the margin of the wound.
• A narrow, circular rim of abrasion may be present due to gases entering the wound and pressing the skin against the muzzle.
• Over bone, gases cannot disperse easily, causing splits (lacerations) of the skin in a radial pattern.
• Wadding or plastic shot containers may be recovered from the wound track.
• Tissues along the wound track may be blackened, and surrounding tissues pinker than normal (carboxyhaemoglobin theory).

Close Discharge

• Within a few centimeters of the skin surface.
• Similar appearance to contact wounds, but muzzle gases can escape, so no muzzle mark (Figure 9.7).
• More smoke soiling and burning of skin, with singeing and clubbing of melted hairs (Figure 9.8).
• Powder 'tattooing' due to burnt and burning flakes of propellant causing tiny burns on the skin.
• Cannot be washed off; wads often found in the wound track.

Intermediate Ranges

• Between 20 cm and 1 m.
• Diminishing smoke soiling and burning of the skin, but powder tattooing may persist.
• The spread of shot begins, causing an irregular rim to the wound ('rat-hole' or 'scalloping').
• Additional injuries from wads or plastic shot containers may be seen (Figure 9.9).
• Substantial tissue damage may occur when both barrels are fired simultaneously (Figure 9.10).

Longer Ranges

• Over 1 m.
• Smoke damage and tattooing are generally absent.
• The nature of injuries depends on the spread of shot, which depends on barrel construction.
• Satellite pellet holes appear around the main central wound at 2-3 m.
• Document the spread of shot and perform test firings with identical ammunition to establish range.
• Estimates based on the ratio of spread diameter to range are unreliable.

Long Ranges

• Greater than 20-50 m.
• Uniform peppering of shot; rarely fatal but can cause life-changing injuries (e.g., loss of eyes) (Figure 9.11a-c).

Exit Wounds

• Shotguns rarely produce exit wounds when fired into the chest or abdomen, although single-pellet exit wounds can be seen.
• Exit wounds can be seen when a shotgun is fired into the head, neck, or mouth.
• The exit wound may be a huge ragged aperture, and the skull may explode with the gas pressure, ejecting brain tissue (Figure 9.12).

Wounds from Rifled Weapons

• Bullets fired from rifled weapons, generally at a higher velocity than pellets from a smooth-bore weapon, will commonly cause both an entry and an exit wound.
• Bullets may be retained due to energy dissipation.
• Wound severity is related to bullet construction, trajectory, and the properties of traversed body tissues.
• The bullet has an upper limit of wounding potential derived from its mass and velocity.

Entrance and Exit Wounds

• Contact wounds are generally circular, unless over a bony area where splitting caused by propellant gas is common (Figure 9.13).
• A muzzle mark may be present if the gun is pressed hard against the skin.
• Slight escape of smoke and local burning of skin and hair may occur if the gun is not pressed tightly.
• Bruising around the entry wound is common (Figures 9.14 and 9.15).
• Close range (up to 20 cm): some smoke soiling and powder burns, and skin and hair may be burnt.
• The shape of the entry wound indicates the angle of discharge: a circular hole indicates a right angle, while an oval hole indicates a more acute angle.
• Entry wound: skin is inverted, the defect is slightly smaller than the missile diameter due to skin elasticity.
• An 'abrasion collar' or 'abrasion rim' is caused by the friction, heating, and dirt effect of the missile.
• Bruising may or may not be associated with the wound.

Longer ranges

• Discharge >1 m: no smoke soiling, burning, or powder tattooing.
• Extreme ranges: the entrance wound will have the same features of a round or oval defect with an abrasion collar (Figure 9.16).
• At extreme ranges, or following a ricochet, the bullet may wobble and tumble, resulting in larger, more irregular wounds.
• The exit wound of a bullet is usually everted with split flaps, often resulting in a stellate appearance (Figure 9.17).
• No burning, smoke, or powder soiling is evident.
• Distorted or fragmented bullets, or fractured bone, may cause considerably larger and more irregular exit wounds.
• Fragments of bullet or bone may cause multiple exit wounds.
• Where skin is firmly supported, the exit wound may be as small as the entrance and may fail to show the typical eversion.
• It may also show a rim of abrasion, although this is commonly broader than that of an entry wound.

Internal effects of bullets

• The severity depends upon their kinetic energy.
• Low-velocity, low-energy missiles cause simple mechanical disruption.
• High-velocity bullets cause more damage due to the transfer of large amounts of energy, forming a temporary cavity in the tissues.
• Especially pronounced in dense organs, such as liver and brain.
• Cavitation is exacerbated by the radial stretching of tissues.
• The importance of an adequate description of gunshot wounds at autopsy is illustrated very well by the ongoing controversy surrounding the death of US President John F Kennedy in 1963 (Box 9.2).

Air Weapons, Unusual Projectiles and Other Weapons

Air Guns and Rifles

• Air weapons rely upon the force of compressed air to propel the projectile, usually a lead or steel pellet although darts and other projectiles may be used.
• Three common ways to compress gas:
  • Compression of a spring (low powered).
  • Repeated movements of a lever to pressurize an internal cylinder (more powerful).
  • Internal cylinder charged by connecting to a pressurized external source.
• The barrel may or may not be rifled.
• Energy depends on gas compression method.
• Injuries depend on projectile design; entry wounds from standard pellets often indistinguishable from standard bullets.
• The relatively low power of these weapons means that the pellet will seldom exit, but if it does so, a typical exit wound with everted margins will result.

Miscellaneous Firearms and Weapons

• Other implements may mimic firearm effects.

Kinetic Energy Devices (KED)

• Used in public disorder situations to dissuade or prevent a behaviourally disturbed person from harming others.
• Not intended to cause serious or life-threatening injury, although such injuries and fatalities do occur.
• Known by various names: plastic bullets, rubber bullets, baton rounds, impact rounds, attenuating energy projectiles (AEP).
• Made from materials of lower density than standard bullets, larger, and fired at lower velocities.
• Accuracy of targeting is crucial.
• Projectiles are often cylinders made of rubber, plastic, wood, or foam.
• 'Beanbag projectile': a fabric bag filled with compliant material that flattens on impact to maximize surface contact.
• The approved AEP (designated as L60A2) is fired from a 37 mm breech loaded weapon.
• The approved launcher is the Heckler and Koch L104A2, equipped with an approved L18A2 optical sight.
• Operational use in the UK police service is limited to authorized officers who have been specifically trained in use of the system.
• A typical impact round is about 100 mm long, 35 mm in diameter and when discharged has a muzzle velocity of -69 ms-1.
• Marks left on the skin surface by KEDs may be patterned and distinctive to that particular device.
• Vulnerable areas: head, thorax, abdomen.

Stud Guns

• Used in the building industry to fire steel pins into masonry or timber using a small explosive charge.
• Accidental injuries are more common.
• The skin wound often appears similar to many small-calibre entry wounds.

Humane Killers

• Used in abattoirs and by veterinary surgeons to stun animals.
• May fire a small-calibre bullet or a 'captive bolt'.
• Accidental discharges are recorded and may cause serious injury or death.

Bows and Crossbows

• Used recreationally but also as weapons.
• Fire arrows or bolts.
• The shape of the entrance wound depends on the type of arrowhead.
• The energy produced is extremely variable.
• Wounds can appear similar to those caused by standard bullets.

Determination of Accident, Suicide or Murder

• Crucial to determine circumstances of firearm injury death.
• Effective investigation required under human rights law if police or security services are involved (Box 9.3).
• Consider the possibility of 'staging' of homicide.
• Suicidal wounds:
  • Accessible site and range of the deceased's arm.
  • Weapon present at the scene.
  • Deceased's DNA or fingerprints on the weapon.
  • Most commonly in the mouth, below the chin, on the front of the neck, the centre of the forehead or, more rarely, the front of the chest over the heart.
  • Discharges into the temples are almost unique to handguns and are usually on the side of the dominant hand, but this is not an absolute rule.
  • People rarely shoot themselves in the eye or abdomen or in inaccessible sites such as the back.
  • It is unusual for females to commit suicide with guns and females are rarely involved in firearms accidents.
• A single gunshot injury could be either accident or homicide if suicide can be ruled out.
• Multiple firearm wounds strongly suggest homicide.
• A full medicolegal investigation is required.
• It is most likely that severe damage to the brain, heart, aorta and any number of other vital internal organs will lead to rapid collapse and death.

Evidence Recovery

• In the living, prioritize saving life.
• Document original injury appearances and take good-quality images before any surgical cleaning or operative procedures are performed.
• Record the nature and direction of possible wound tracks, and their length.
• Preserve foreign objects, bullets or shot, and skin removed from the margin of a firearm wound during treatment.
• Contact police (with consent) if surgical intervention is required.
• Examine and take samples from those arrested.
• Apply standardized and approved processes to all forms of trace evidence collection.
• Apply the same rules to post mortem recovery.
• Take swabs of the victim's hands.
• Obtain accurate drawings and measurements of the wound.
• Take distant and close-up photographs of each injury with an appropriate scale in view.
• All firearm wounds, whether fatal or not, must be reported to the police.

Blast Injuries

• Result from armed conflict and terrorist activity.
• Sources: improvised explosive devices (IEDs), car bombs, suicide bombers.
• The nature of the explosive device may alter the nature of injury.
• The position or activity of the individual may influence injury and outcome.
• Energy release may cause death and disruption over a wide area.
• Devices in confined spaces influence injury patterns.
• The energy of an explosion decreases rapidly as the distance from the epicentre increases.
• Generation of huge volumes of gas.
• Compression wave sweeps outwards.
• A minimum pressure of about 700 kPa (100 lb/inch2) is needed for tissue damage in humans.
• Pressure effects upon the viscera.
• Rupture and hemorrhage in areas with an air-fluid interface.
• Blast injuries can be categorized as primary to quaternary injuries.
  • Primary injuries: effect of transmitted blast waves on gas-containing structure.
  • Secondary injuries: impact of airborne debris.
  • Tertiary injury: transposition of the entire body due to blast wind or structural collapse.
  • Quaternary injuries: burns.
  • Quinary blast injuries: the clinical consequences of post-detonation environmental contamination such as bacteria.

Effects from Explosive Devices

• Burns from the explosion and fires started by the bomb.
• Missile injuries from bomb casing parts, contents, or shrapnel.
• Peppering by small fragments of debris and dust (Figure 9.20).
• Various injuries due to structural collapse.
• The body impacting against other structures or objects.
• Injuries and death from vehicular damage or destruction.

Mass Disasters

• Investigation of the scene is complex.
• Triage to preserve life and evacuate casualties, while maintaining a crime scene.
• Multiprofessional teams are required to ensure evidence integrity.
• Post mortem radiology is essential to identify unexploded ordinance.
• Identification of deceased is important.
• Challenging to identify suicide bombers (Figure 9.21).
• Treatment of casualties and triage is the first consideration.

Triage

• Box 9.5 illustrates the widely accepted colour-code system used to categorise disaster victims in the field.
• 'Expectant' category can be the most challenging.
• In 2017, the World Medical Association (WMA) revised its Statement on Medical Ethics in the Event of Disasters; (Box 9.6) the key points are summarised.
• The International Committee of the Red Cross has provided advice on the management of the dead.
• Investigation of causes of death and identification of the dead are specialist operations.
• A team of pathologists inspects each body and records all clothing, jewellery and personal belongings still attached to the bodies.
• The body, or body part, is then carefully examined for every aspect of identity, including sex, race, height, age and personal characteristics.
• All these details are recorded on standard forms and charts and the information is sent back to the identification teams, who can compare this post mortem information with ante mortem information obtained from others including relatives, friends and work colleagues.
• A post mortem examination is usually performed to determine the cause of death.