Gunshot and Explosive Injuries

Firearm Basics & Wound Ballistics - Bullet Points 101

• Firearm Types:
  • Rifled: Handguns, rifles (impart spin for stability, accuracy).
  • Smoothbore: Shotguns (fire multiple pellets or single slug).
• Ammunition (Cartridge):
  • Components: Bullet (projectile), casing, propellant (e.g., gunpowder), primer (ignites propellant).
• Wound Ballistics Principles:
  • Kinetic Energy (KE): $KE = 1/2 mv^2$; velocity is the most significant factor.
  • Temporary Cavity: Transient outward stretch of tissues due to energy transfer; causes significant damage.
  • Permanent Cavity: Actual path of tissue destruction by the bullet.
  • Bullet Behavior: Yaw (deviation from axis), tumbling, fragmentation (all ↑ tissue damage).
  • Tissue Factors: Density and elasticity of tissue.

⭐ Bullet velocity has a squared relationship with kinetic energy ($KE = 1/2 mv^2$), making it the primary determinant of wounding capacity over bullet mass alone.

Gunshot Entry Wounds - Marking the Spot

• General Features:
  • Shape: Round/oval, often smaller than bullet diameter (skin elasticity).
  • Abrasion Collar (Rim): Friction/indentation by bullet. Concentric (perpendicular entry), eccentric (angled entry).
  • Grease/Bullet Wipe: Grime/lubricant from bullet on wound edge.
• Range of Fire Indicators:
  • Contact: Muzzle imprint, soot & searing in track, carboxyhemoglobin (cherry-red tissue), stellate (if over bone).
  • Close Range (< 15-20 cm): Soot (on skin, wipeable), tattooing/stippling (powder in skin, not wipeable).
  • Intermediate Range (15-20 cm to 60-90 cm): Tattooing present; soot absent.
  • Distant Range (> 60-90 cm): Only abrasion collar & bullet wipe.
• Skull Entry Wounds:
  • Exhibit internal bevelling (defect wider on inner table).

  ⭐ Skull entry wounds show a "punched-in" appearance on the outer table and characteristic internal bevelling on the inner table.

Gunshot Exit Wounds & Internal Path - In and Out

• Exit Wounds:
  • Often larger, more irregular than entry; everted edges.
  • Slit-like, stellate, or round; variable shape.
  • Absent: abrasion collar, soiling, blackening, tattooing.
  • Shored exit: if skin supported (e.g., tight clothing, wall), may show imprint.
• Internal Path (Track):
  • Reveals bullet's course, organ damage.
  • Primary cavity: direct tissue destruction.
  • Secondary (temporary) cavity: kinetic energy transfer; wider injury.
  • Bullet may fragment or ricochet (off bone).
  • Damage depends on: velocity, bullet type, tissue density.

⭐ Exit wounds are typically larger and more irregular than entry wounds because the bullet often tumbles or deforms after passing through tissues.

Explosive Injuries - Big Bang Trauma

Explosions cause complex polytrauma via multiple mechanisms. Classified by order: Low (subsonic, e.g., gunpowder) vs. High (supersonic, e.g., TNT, RDX).

• Primary Blast Injury (PBI): Direct effect of overpressure wave.
  • Affects gas-filled organs: Lungs (blast lung), ears (tympanic membrane rupture), gastrointestinal tract (hemorrhage, perforation).
  • Brain: Concussion (shell shock), cerebral air embolism.
• Secondary Blast Injury: From energized fragments (bomb casing, environmental debris).
  • Penetrating trauma, lacerations, fractures.
• Tertiary Blast Injury: Victim propelled by blast wind into solid objects.
  • Blunt trauma, fractures, head injuries, traumatic amputations.
• Quaternary Blast Injury: Other explosion-related injuries.
  • Burns (flash, flame), crush injuries, asphyxia from dust/fumes, toxic exposures.
• Quinary Blast Injury: Delayed effects/systemic responses.
  • Hyperinflammatory state, infections, multi-organ failure, exacerbation of chronic illness.

⭐ Blast lung (pulmonary contusion, edema, alveolar hemorrhage) is the most common fatal PBI among initial survivors and a critical determinant of outcome.

📌 Mnemonic (Blast Organs): "Blast Lungs Ears Guts" (Brain, Lungs, Ears, GI Tract) for primary blast injury sites.

High‑Yield Points - ⚡ Biggest Takeaways

• Range of fire in gunshot wounds is determined by presence/absence of soot, stippling (tattooing), and muzzle imprint.
• Entrance wounds: Typically smaller, circular, with an abrasion collar and internal bevelling (skull). Exit wounds: Usually larger, irregular, everted, with external bevelling (skull).
• Stippling/Tattooing: Caused by unburnt/partially burnt powder particles hitting skin; indicates intermediate range and is absent in distant shots.
• Shotgun injuries: Characterized by pellet dispersion which ↑ with range; choke of the gun influences pellet pattern. Wad injuries may be present.
• Explosive injuries are classified into: Primary (blast wave overpressure), Secondary (projectiles), Tertiary (victim displacement), and Quaternary (burns, toxins, crush injuries).