Wound Ballistics and Firearm Injuries
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Direct answer
A bullet destroys tissue by crushing along its track and by stretching it radially, the temporary cavity of high-velocity rounds explains devastation far beyond the visible hole. Forensically the work is range and direction: the entry wound classically shows an abrasion collar with grease or soiling, the exit wound is everted without a collar, and the burning, soot and unburnt-powder tattooing around the entry quantify the distance from muzzle to skin. Shotguns add a spread geometry — one hole at contact range, a ragged margin of separated pellets at intermediate range, and a scattering of individual pellet wounds at distant range — which lets the examiner reconstruct the shot from the skin alone.
What you must remember
- Ballistics divides into internal (inside the weapon), external (in flight) and terminal or wound ballistics (in tissue) — a guaranteed one-mark sequence.
- Rifled weapons impart spin through lands and grooves; calibre is measured between opposite lands; the fired bullet carries class and individual marks matching the barrel.
- Entry wound: round to oval defect with a marginal abrasion collar plus a grease or dirt collar; edges are inverted.
- Contact wound over bone: gases strip the periosteum and split the skin into a stellate or cruciate tear with a muzzle imprint — the wound may look larger than the exit.
- Soot (blackening) is wipeable and reaches roughly 15–30 cm; tattooing (stippling from unburnt and partially burnt powder) cannot be wiped off and may be seen out to about 45–60 cm, weapon dependent.
- Exit wounds are everted, larger and more irregular, lack abrasion or grease collars, and shored exits (skin supported by belt or wall) may mimic entries with a broad abrasion rim.
- Shotgun: at contact range a single hole with scalloped margin; wads and felt filler may be recovered from the wound up to about 1–3 m; beyond that pellets separate, the spread widening roughly a few centimetres for every additional metre of range.
- High-velocity rounds (above roughly 600–800 m/s) create a temporary cavity with shock-wave damage; low-velocity handgun bullets damage mainly by direct track — and gunshot residue on hands is tested by SEM-EDX on tape lifts, the old paraffin test being obsolete.
Reading one gunshot wound at autopsy
Take a chest wound examined at autopsy. First photograph with a scale, then describe without interpreting: an oval defect, margins inverted, a rim of abrasion and soiling around part of the circumference. Probe the track — this is the only proof of direction — and follow it through rib, lung and out through a larger, everted, collar-less defect at the back. The pairing already says the front wound is the entry. Now look at the surroundings under a dissecting lens: dry wipe a grey film — it lifts, so soot; note punctate dots that do not wipe — tattooing.
Reconstruct the story last: soot together with a muzzle imprint means near-contact; with all residue absent, the weapon stood beyond a metre. Recover the bullet with rubber-coated forceps — never bare metal — because the engraving on its jacket is the firearm's fingerprint, and preserve the clothing, since powder may be caught in fabric even when skin shows none.
Where candidates slip
The deadliest assumption is "entry is always smaller than exit". A contact wound over the temple is stellate and huge; a shored exit against a tight belt is slit-like with a misleading abrasion rim. Direction is proved by the wound track and clothing defects, never by size alone. The second slip is quoting fixed centimetre boundaries for soot and tattooing as if universal: barrel length, ammunition and target angle all shift them, so the safe phrasing is "soot suggests a range of centimetres, tattooing tens of centimetres". Third, forgetting that the calibre cannot be read off the skin wound — skin elasticity shrinks the defect below bullet diameter; the recovered bullet or the bone defect is the measurable one.
Frequently asked questions
Which features distinguish an entry from an exit wound?
Entry: inverted edges, abrasion collar, grease collar, possible soot or tattooing; exit: everted, punched-out or ragged edges, larger and irregular, no collars or residue.
What is tattooing and up to what range is it seen?
Tattooing is dermal stippling by unburnt and partly burnt powder grains driven into skin; it cannot be wiped off and typically indicates a range up to about half a metre.
Why may a contact wound be larger and stellate?
Muzzle gases enter beneath the skin, strip periosteum from bone and blow back out, splitting the skin, often leaving a muzzle imprint around a cruciate tear.
How is range estimated in shotgun injuries?
By spread: a single scalloped hole at contact, scattered satellite pellets with increasing range, wadding injuries within the first couple of metres, and the pattern width growing with distance.
Which test detects gunshot residue on hands today?
Scanning electron microscopy with energy-dispersive X-ray analysis of tape lifts, detecting primer particles of lead, antimony and barium; the paraffin or dermal nitrate test is obsolete.