Firearm & Gunshot Injuries

Firearm injuries are among the most reliably tested topics in Forensic Medicine for NEET PG. The core skill is reading a wound like a forensic pathologist: distinguishing entry from exit, estimating range of fire, and identifying the weapon type from the wound and recovered projectile. Master the cut-off distances and the named features and you can usually answer any vignette.

Basic terminology & weapon classification

A firearm is a weapon that propels a projectile by the rapid expansion of gases from burning propellant (gunpowder). Understanding the weapon dictates the wound.

Feature	Rifled (high-velocity)	Smooth-bore (shotgun)
Bore	Spiral grooves (rifling)	Smooth
Projectile	Single bullet	Multiple pellets / shot
Examples	Revolver, pistol, rifle	Shotgun (12-bore common)
Velocity	High (300–900 m/s)	Lower (~400 m/s)
Markings on bullet	Lands & grooves	None
Wound	Single entry	Single at close range; multiple at distance

Rifling consists of lands (raised ridges) and grooves (depressions) cut spirally inside the barrel. Rifling imparts spin (gyroscopic stability) to the bullet, improving accuracy and range. The rifling leaves characteristic class (calibre, number/direction/width of lands & grooves) and individual (microscopic striations) marks on the bullet — the basis of ballistic matching.

High-yield: Rifling gives spin/gyroscopic stability and leaves striation marks → enables individualisation of the weapon. Direction of twist is usually clockwise (right-handed).

Components of a cartridge: primer (percussion cap), propellant (smokeless/black powder), bullet (projectile), and the cartridge case. Shotgun cartridges additionally contain wads (felt/plastic discs separating powder from shot) and multiple pellets.

Choking is the narrowing of the muzzle end of a shotgun barrel to reduce pellet dispersion and increase effective range.

Components of the gunshot wound & the "soot–powder" story

When a firearm discharges, several things emerge from the muzzle in sequence and with different ranges of travel. These are the basis of range estimation:

1. Bullet/pellets — travel farthest; cause the actual perforating injury.
2. Flame/hot gases — travel only a few cm → cause burning/singeing of hair & charring.
3. Smoke/soot (smudging, blackening) — travels up to ~15–30 cm → soot deposition that can be wiped off.
4. Unburnt/partially burnt powder grains → cause tattooing (stippling) — punctate abrasions that cannot be wiped off.
5. Carbon monoxide → produces cherry-red discolouration of wound margins (carboxyhaemoglobin) in close-range shots.
6. Metal/primer residues (Pb, Sb, Ba) → detected chemically (dermal nitrate test, AAS).

High-yield: Blackening/smudging (soot) is WIPEABLE; tattooing (powder grains) is NOT wipeable. This single distinction is repeatedly asked.

Grease/dirt collar (grease ring) — a ring of grease and dirt wiped off the bullet surface as it perforates skin, deposited just outside the abrasion collar. Indicates the wound is an entry wound regardless of range.

Entry vs exit wound — the central comparison

This is the single most examined table in the entire topic.

Feature	Entry wound	Exit wound
Size	Usually smaller than bullet (skin retracts/elastic)	Usually larger, irregular
Margins	Inverted	Everted
Abrasion (contusion) collar	Present	Absent
Grease collar	Present	Absent
Singeing/blackening/tattooing	May be present (range-dependent)	Absent
Shape	Usually round/oval	Irregular, slit-like, stellate
Cherry-red colour (CO)	May be present	Absent
Bleeding (external)	Less	More
Bone bevelling (skull)	Internal (cone widens inward)	External (cone widens outward)

High-yield: In the skull, entry wound shows internal bevelling, exit shows external bevelling — the cone of fracture widens in the direction of bullet travel. This is a classic single-best-answer.

Important exceptions:

• Entry wound can be larger than the bullet in contact wounds over bone (e.g., temple) due to gas expansion → stellate/cruciate wound.
• Abrasion collar (contusion collar / margin of abrasion) = epidermis scraped off as the bullet indents and perforates → the most reliable single feature of an entry wound regardless of range.
• An exit wound may be shored (supported exit / "shored exit wound") when skin is pressed against a firm surface (belt, wall, floor) → develops an irregular abrasion margin and can mimic an entry wound.

Range of fire — the cut-offs you MUST memorise

Range estimation rests on which muzzle products reach the skin. These are the most testable numbers in forensic ballistics. (Values are approximate and weapon-dependent.)

Range	Key features at skin
Contact (muzzle pressed)	Burning, blackening, tattooing all driven INTO wound; CO cherry-red; muzzle imprint/abrasion; stellate over bone; dirty wound margins
Close / near-contact (< ~15 cm)	Singeing of hair, blackening (soot), tattooing all present around wound
Intermediate (~15–60 cm, up to ~1 m)	Tattooing present, blackening/singeing absent (beyond soot range)
Distant (> ~1 m / ~ >60–90 cm)	Only the mechanical wound (no soot, no tattooing, no singeing); grease/abrasion collar still present

Approximate maximal ranges of each component (smokeless powder, handgun): flame/singeing ≈ 5–8 cm; soot/blackening ≈ 15–30 cm; tattooing ≈ 60 cm–1 m. Beyond ~1 m only the abrasion + grease collar remain.

High-yield: Tattooing is the LAST powder feature to disappear with increasing range → its presence indicates the shot was fired within ~1 metre. Absence of tattooing/blackening with only a clean entry + grease collar = distant shot.

Stepwise approach to range estimation:

See burning + blackening + tattooing + muzzle imprint → Contact/near-contact → then check for singeing only (no imprint) = close → then tattooing without blackening = intermediate → then clean wound, grease collar only = distant.

Contact wounds — special features

• Hard contact over bone (skull, temple): expanding gases enter between skin and bone → balloon the skin back against the muzzle → stellate / cruciate laceration; muzzle imprint (contusion abrasion in shape of muzzle) — strong evidence of contact and an indicator of suicide when over an accessible "site of election".
• Soft tissue contact (abdomen): circular wound with soot inside the track.
• CO binds Hb in the wound track → cherry-red muscle and carboxyhaemoglobin detectable.

Shotgun (smooth-bore) wounds — range by pellet spread

For shotguns, range is judged by degree of pellet dispersion and presence of wads:

Range	Wound pattern
Contact / very close (< ~1 m)	Single large circular hole ("rat-hole"); margins burnt/blackened; wads enter wound
~1–3 m	Central hole with crenated (scalloped) margin; few satellite pellet holes; wads near surface
~3–6 m	Multiple separate pellet holes around a larger central defect ("rose petal"/"satellite" pattern)
> ~6–10 m	Pellets fully dispersed — uniform peppering, no central hole

A rough rule: spread of pellets in cm ≈ range in metres (varies with choke). Wads travel up to ~2–3 m and their position helps confirm a close shot; recovered wads/cup can also indicate gauge.

High-yield: Shotgun at contact range → single ragged hole with inverted, soot-stained, burnt margins (NOT scattered pellets). Scattered satellite pellet holes = a more distant discharge.

Other wound types & special situations

• Graze wound: bullet travels tangentially → elongated abrasion/laceration; direction told by skin tags pointing back toward the firearm.
• Tandem / piggy-back bullet: two bullets fired sequentially, second pushes a lodged first → single entry, two bullets.
• Ricochet bullet: deflected off a surface → irregular, larger, often "keyhole" entry; deformed bullet.
• Keyhole wound (skull): tangential entry → combined entry-exit defect with both internal and external bevelling at one site.
• Dum-dum / expanding (hollow-point) bullets: mushroom on impact → large, devastating exit wounds; prohibited in warfare (Hague Declaration).
• Souvenir bullet: retained, encapsulated bullet found incidentally years later.

Investigations & laboratory tests

• Dermal nitrate (paraffin) test / Gonzales test: detects nitrates from unburnt powder on the hand/skin (pink colour with diphenylamine). Non-specific (fertilisers, tobacco, urine also give positives) — now largely obsolete.
• Harrison & Gilroy test: detects lead, antimony, barium (primer metals).
• Atomic Absorption Spectrophotometry (AAS) / Neutron Activation Analysis / SEM-EDX: modern, sensitive detection of gunshot residue (GSR) — Pb, Sb, Ba on hands.
• Walker test: detects nitrites around the wound to map powder distribution and estimate range.
• Radiology (X-ray): localises retained bullet/pellets, "lead snowstorm" with fragmenting bullets; mandatory before exploration.
• Comparison microscopy: matches recovered bullet striations to a test-fired bullet from the suspect weapon (individualisation).
• Histology: vital reaction (haemorrhage, inflammation) confirms the wound was antemortem.

High-yield: Dermal nitrate test detects NITRATES and is non-specific/unreliable; modern GSR analysis (AAS/SEM-EDX) detects the primer metals lead, antimony, barium.

Determining manner of death (medico-legal)

Pointer	Suicide	Homicide	Accident
Site	"Site of election" (temple, mouth, precordium)	Any, often back/inaccessible	Variable
Range	Contact/close	Any, often distant	Variable
Number of wounds	Usually single (multiple possible)	Often multiple	Single
Hand	Cadaveric spasm holding weapon	Weapon absent/displaced	—
Muzzle imprint	Often present	Less likely	—

Site of election for suicidal firearm wounds: right temple (right-handed), mouth, centre of forehead, precordium. Contact wound + accessible site + cadaveric spasm strongly suggest suicide.

Complications

• Immediate: haemorrhage, hypovolaemic shock, organ perforation (cardiac, great vessels, lung → tension pneumothorax/haemothorax), CNS injury.
• Infective: wound sepsis, gas gangrene/tetanus (dirty wound, retained wad/clothing), osteomyelitis.
• Delayed: lead poisoning (plumbism) from a retained bullet in a joint/CSF; embolisation of a bullet via vessels; pseudoaneurysm; AV fistula; foreign-body granuloma; PTSD.

Key differentials

• Entry vs exit wound (most important; use abrasion + grease collar, bevelling).
• Shored exit vs entry — shoring history & surface contact.
• Contact firearm wound vs blast/explosion injury — pattern of soot, fragments.
• Stab/incised wound vs firearm graze — clean edges vs abrasion.
• Self-inflicted vs homicidal — site, range, cadaveric spasm.

Recently asked / exam angle

• "Wipeable vs non-wipeable" → blackening wiped off; tattooing not.
• Internal bevelling = entry, external bevelling = exit (skull) — recurring single-best-answer.
• Abrasion (contusion) collar = most reliable feature of an entry wound.
• Tattooing present ⇒ shot fired within ~1 m; clean wound + grease collar only ⇒ distant.
• Rifling imparts spin (gyroscopic stability) and leaves striations enabling weapon identification.
• Cherry-red colour of wound margins in contact wounds = carboxyhaemoglobin (CO).
• Dum-dum bullet = expanding/mushrooming → large exit; banned in war.
• Shotgun contact wound = single ragged burnt hole, NOT scattered pellets.
• GSR primer metals = Lead, Antimony, Barium; dermal nitrate test detects nitrates & is non-specific.
• Grease collar confirms entry irrespective of range.
• Muzzle imprint / stellate wound over bone = contact range, suggests suicide at site of election.
• Walker test maps nitrites → range estimation; Harrison & Gilroy detects primer metals.

Rapid revision

1. Entry wound: smaller, inverted margins, abrasion collar + grease collar present.
2. Exit wound: larger, everted, irregular/stellate, NO abrasion or grease collar.
3. Skull → entry = internal bevelling, exit = external bevelling (cone follows bullet).
4. Blackening (soot) = WIPEABLE; tattooing (powder grains) = NOT wipeable.
5. Singeing ≈ up to 8 cm; blackening ≈ up to 15–30 cm; tattooing ≈ up to ~1 m.
6. Tattooing is the last feature lost with range → presence means shot within ~1 metre.
7. Contact wound: muzzle imprint, stellate over bone, CO cherry-red margins, soot inside track.
8. Distant shot = clean entry + grease/abrasion collar only, no soot/tattooing.
9. Rifling = lands & grooves → spin/gyroscopic stability + striation marks for matching.
10. Shotgun contact = single ragged "rat-hole"; spread (cm) ≈ range (m).
11. GSR primer metals = Lead, Antimony, Barium; modern test = AAS/SEM-EDX; nitrate test non-specific.
12. Dum-dum/hollow-point bullets mushroom → massive exit wounds; banned in warfare.