Gunshot Wounds Flashcards
Types of guns
Rifled weapon fire single bullet - handguns - rifles - grooved spiralled long barrel Smooth bore weapons fire multiple lead pellets - shotgun
Ballistics motion of projectiles
Interior ballistics - travel within weapon Exterior ballistics - travel in air Terminal ballistics - penetration of solids Wound ballistics - penetration of tissues
Types of interior ballisitcs
Rifling marks on bullet - class characteristics - make/model - individual characteristics - unique to gun Cartridge case - extractor Primer cap - firing pin Fingerprints
Effects of kinetic energy in bullets
Large velocity gives high energy on impact KE = 1/2 mass of bullet x velocity^2 Double mass of bullet -> double energy Double velocity -> quadrupled energy Wounding effect due to transfer from bullet to tissues - miss = no energy transferred - exit = not all energy transferred - no exit = all energy transferred
Types of small firearms
Shotguns - smooth bore Handguns Rifles Submachine guns Machine guns
Rifling marks
Lands and grooves inside barrel give specific characteristics Class characteristic of weapon - number of lands and grooves - width - depth - degree of twist - direction of twist Individual characteristics of weapon - imperfections on lands and grooves due to use
Types of handguns
Single shot pistols
Derringers
Revolvers
Auto-loading pistols
Features of revolvers
Rifled barrel Fired from hand Revolving cylinder Several chambers Types - solid frame - swingout - chamber spins outside ways - breaktop - load from behind
Features of auto-loading pistols
Rifled barrel
Fired from hand
Removeable magazine stores cartridges - sits in handle
Mechanism for autoloading - fires 10-15 shots one after each other
Features of rifles
Rifled barrel Fired from shoulder Single projectile Types - single shot - bolt action - lever action - pump action - autoloading
Features of sub-machine guns
Rifled barrel
Fired from shoulder or hip
Fires pistol ammunition
Capable of fully automatic fire
Features of machine guns
Rifled barrel
Fired by individual or crew
Fires rifle ammunition
Capable of fully automatic fire
Parts of small arms ammunition
Bullet
Propellant
Primer
Cartridge case
Handgun ammunition
A range of calibre - .22 to .5 inch
Blanks has case, propellant with a plastic cap but no bullet
Different tip types
Features of small arms ammunition
Cartridge case
- composed of brass cylinder
- filled by propellant
- expands to fill chamber on discharge
Primer
- lead, barium and antimony compounds
- shock-sensitive chemical compound explodes on impact by firing pin
- flame secondarily ignites propellant
- 2 types - centrefire (firing pin strikes centre) and rimfire (firing pin strikes anywhere on base)
Propellant
- smokeless powder - nitrocellulose +/- nitro-glycerine
- burns to produce large volume of gas under pressure
- forces projectile down and out of barrel
- formulations - discs, flakes, cylinders, balls or flattened balls
Features of lead bullets
Usually lead but can be alloyed with tin/antimony
May have thin copper gilding
Used in revolvers and .22 rimfire cartridges
Types
- round nose
- wadcutter
- hollow point - mushroom and stay within animal preventing secondary damage and injury
Features of jacketed bullets
Lead or steel core
Encased in jacket of CuZn, CuNi or Al
Used in auto-loading pistols and HV rifles
Types
- full metal jacket - HV military rifle
- partial metal jacket - hunting and autoload pistol
- semi-jacketed hollow soft/point - hunting
- silvertip - all
Wounding mechanisms from bullets
Direct laceration - permanent cavity
Temporary cavity > 800m/s
- opens in wake of bullet and collapse on exit
- wide zone of haemorrhage around wound tack
- dense inelastic organs (liver) may rupture
Shockwaves may rupture gas-filled organs (bowel, bladder)
Secondary projectiles - bone fractures cause injury
Discharge gases at contact range
Gunshot signs range
Flame - 5cm
Smoke - 15cm - billows out so wider radius
Tattooing - 50cm - burnt propellant marks skin
Features of entry wounds
Abrasion and stretching of skin from contact
Chips away bone as exits cause conical appearance
Features of exit wounds
Smaller hall on entry side and larger on exit side - conical shape
Exit defect in skin larger than bullet due to skin being stretched
Skin surface characteristics of gunshot wound
Muzzle imprint Hot gases - singeing Soot - smudging Propellant - tattooing Bullet - skin defect - abrasion of margin - microtears - bullet wipe
Features of contact range wound
Soot and propellant seared into margins
Loose contact - sideways escape of soot-laden gas
Angled contact - eccentric soot stain
Features of near contact range wound
Few cm Soot and propellant seared into margins No tattooing Peripheral ring of soot staining - soot reached 20-30cm - can be wiped off
Features of intermediate range wound
Few cm to 1m - arms reach
Powder tattooing
- unburnt or partially burnt propellant grains
- individual reddish-brown punctate abrasions
- vital reaction - rim of bruising
- eccentric pattern if angled entry
- spread depends on powder, range and barrel
- reaches up to 30-40 cm
Features of distant range wound
Beyond 1m - beyond arm's length No flame effect No soot effect No propellant tattooing Bullet is on its own Skin defect with marginal abrasion - circular if impact at right angle - elliptical if impacting at another angle
Entry vs exit wounds
Entry - circular defect - diameter < bullet - abraded margin - soot - propellant Exit - irregular shape - diameter > bullet - no abrasion - near exit
Features of gunshot residues
Spheroidal particles of barium, lead and antimony compounds from primer
- condensation and solidification of molten and vaporised primer and bullet materials
Newer lead-free ammunition
Deposited on radial side of firing hand
Cotton tipped swab moistened with HCl or HNO3
Sent for forensic scientific analysis
Formation of gunshot residue
Hammer within firearm strikes outside of priming cap crushing explosive
Shock-sensitive chemical compound explodes igniting secondary charge of gunpowder
Temperatures exceed 2000°C
Unburnt powder and vaporised metallic components from priming cap remain within recently formed gasses
Increase in pressure causes ejection of bullet from casing and barrel
Spherical particles formed are composed of elements present in the primer therefore making gunshot residue unique
Shotgun discharge range
Flame - 15cm Smoke - 38cm Powder tattooing - 60cm Wad - 1m Satellite holes - 2m Uniform peppering - 10m
Features of shotguns
Smooth barrel Fired from shoulder Fires multiple pellets Types - single shot - double barrel - over and under - bolt - lever - pump - autoloading
Shotgun gauge
Number of balls of lead exactly fitting the barrel diameter which make up 1lb in weight
- .410 is 10.2mm internal diameter
- 20 gauge is 15mm
- 12 gauge is 18.2mm
- 10 gauge is 21 mm
Features of choke of barrel
Taper towards muzzle keeping shots more closely clustered
Measured as % shot striking within 30” target circle at range of 40 yd
- cylinder = 30%
- improved cylinder = 40%
- modified choke = 50%
- full choke = 60%
Parts of shotgun ammunition
Crimped plastic tube Shot Wad - plastic Powder Primer Brass head plate
Shotgun power piston
Plastic spring shaped wad 12g, 16g and 20g have 4 petals .410 has 3 petals Pushes shot out of barrel Contributes to wound - < 1f not yet opened - 1-3 ft abrasions from petals - > 3 ft folded back - 8-10ft strikes alongside entry Indicates manufacturer and gauge
Features of contact shotgun wound to head
Very mutilating - gas - energy of shot Scalp laceration Skull fracture Brain may be blown out Most pellets and wad may exit
Features of contact shotgun wound to torso
Circular entry = muzzle diameter Muzzle imprint Soot smudging Burning or melting of clothes Cherry pink wound margin - CO
Features of distant range shotgun wound
Small circular defect < 2' No tattooing > 3' Scalloped margins by 3' Satellite holes (fliers) by 4' Cuff of satellite holes by 6' Beyond 10' entry depends on - range - length and choke of barrel - ammunition Test firing required
Features of gunshot suicide
Rare in females Contact wound -> presumption of suicide HV blood splatter on steadying hand GS residues on firing hand Evidence of test firing Sites of election - head = 80% - chest = 15% - abdomen = 5%
Important points in gunshot cases
Beware of artefacts and loss of evident Take X-rays Examine clothing for burns, tattooing and gunshot residue Examine hands - soot - blood - residues Recover projectiles - bullet, pellets - propellant, wadding
Problems with gunshot cases
Shored or partial exit wounds Bullet ricochet out of and within body Separation of bullet jacket and core Projectiles may embolise or move Plastic wad and AI jacket invisible on x-ray X-ray may magnify projectiles Snooker ball effect of pellets
