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Forensic Medicine > Gun Shot Wounds > Flashcards

Gun Shot Wounds Flashcards

1
Q

What type of projectile does a smooth bore weapon fire

A

Multiple lead pellets

Includes shotguns

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2
Q

What is ballistics

A

The study of the motion of projectiles

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3
Q

What type of projectile does a rifled weapon fire

A

Single bullets

Includes handguns and rifles

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4
Q

What are interior ballistics

A

The study of the travel of projectile within the weapon
Includes rifling marks, cartridge case marks from extractor, primer cap marks from firing pin and fingerprints on bullet from loading
Can help identify the weapon a bullet has come from

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5
Q

What are exterior ballistics

A

The study of the travel of the projectile through the air

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6
Q

What are terminal ballistics

A

The study of the penetration of solids by a projectile

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7
Q

What are wound ballistics

A

The study of the penetration of tissues by a projectile

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8
Q

What types of rifling marks might you find on a bullet

A

Class characteristics - scratches which indicate the make/model of weapon
Individual characteristics which are unique to gun - irregularities appear with use

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9
Q

How do you calculate the kinetic energy of a bullet

A

KE = ½ Mass of bullet x Velocity2

Greater the mass of bullet and the greater the velocity the greater the energy (2x and 4x more respectively)

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10
Q

What causes the wounding effect to tissues in a gunshot

A

Caused by the transfer of energy from bullet to the tissues

Bullets are so harmful due to the speed at which they travel - high energy

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11
Q

If the bullet exits the body all of it’s energy has been transferred - true or false

A

False
Not all energy will have been transferred (still has energy to travel out of body)
A bullet that does not exit will have transferred all it’s energy

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12
Q

Which guns are considered ‘small arms’

A 
Shotguns (smooth bore not rifled) 
Handguns
Rifles
Submachine guns
Machine guns
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13
Q

What causes rifling marks on a bullet

A 
Spiraled lands and grooves on the internal surface of the barrel 
Leads to lines/scratches on the bullet 
Can be used to identify class of weapon and even individual weapon
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14
Q

How can you identify the class/model of weapon from the rifling marks

A 
You analyse the: Number of lands & grooves
Width
Depth
Degree of twist
Direction of twist

Should match a specific make/model

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15
Q

How can you identify the individual weapon from the rifling marks

A

Imperfections in the lands/grooves will leave unique rifling marks that can be matched to the weapon
Imperfections caused by firing/use - can change over time with use

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16
Q

Which guns can be classified as handguns

A

Single shot pistols
Derringers
Revolvers
Auto-loading pistols - like glocks

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17
Q

What are the main features of revolvers

A 
Rifled barrel
Fired from hand
Revolving cylinder - spins to load bullets until they run out 
Several chambers
Usually contain around 6 bullets
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18
Q

What are the main types of revolvers

A

Solid frame - hard to load
Swingout - chamber comes out at side
Breaktop - chamber opens on top

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19
Q

What are the main features of auto-loading pistols

A

Rifled barrel
Fired from hand - glocks like on TV
Removable magazine stores cartridges - usually in the handle
Mechanism for autoloading - will fire until magazine is empty
Press trigger each time to fire - not automatic fire

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20
Q

What are the main features of rifles

A

Rifled barrel
Fired from shoulder
Single projectile

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21
Q

What are the main types of rifles

A 
Single shot
Bolt action
Lever action
Pump action
Auto loading
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22
Q

What are the main features of sub machine guns

A

Rifled barrel
Fired from shoulder or hip
Fires pistol ammunition - i.e. not lead bearing
Capable of fully automatic fire

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23
Q

What are the main features of machine guns

A 
Rifled barrel
Fired by individual or crew
Mounted military weapons
Fires rifle ammunition - larger ammo 
Capable of fully automatic fire
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24
Q

What makes up the ammunition required for small arms

A

Bullet at front
Propellant
Primer
Cartridge case around all

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25
Q

Describe the structure of a small arms ammunition cartridge case

A

Composed of a brass cylinder filled with propellent (e.g. gunpowder)
This expands to fill the chamber with gas when fired

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26
Q

Describe the composition of a primer in small arms ammunition

A

It is a shock-sensitive chemical compound which explodes when impacted by the firing pin
Made up of lead, barium & antimony compounds

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27
Q

What are the 2 main types of primer in small arms ammunition

A

Centrefire

Rimfire

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28
Q

What is used in small arms ammunition as propellent

A

Smokeless powder made of nitrocellulose +/- nitroglycerine

Can be in the form of discs, flakes, cylinder, balls or flattened balls

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29
Q

How does the propellent work in small arms ammunition

A

It burns to produce large volume of gas under pressure
Ignited by the primer explosion
This pressure forces projectile(s) down & out barrel

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30
Q

List the main types of lead bullets

A

Round nose
Wadcutter
Hollow point

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31
Q

Describe the structure of a lead bullet

A

Made of lead, alloyed with tin &/or antimony

May have thin copper gilding (thin coating)

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32
Q

Lead bullets are used in which types of gun

A

Used in revolvers and .22 rimfire cartridges

Handguns and rifles

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33
Q

List the main types of jacketed bullets

A

Full metal jacket (HV military rifle)
Partial metal jacket (hunting & auto-load pistol)
Semi-jacketed hollow soft/point (hunting)
Silvertip (Al)

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34
Q

Jacketed bullets are used in which types of gun

A

Used in auto-loading pistols (glocks) and high velocity rifles

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35
Q

Describe the structure of jacketed bullets

A

Have a lead or steel core
Encased in a jacket of CuZn, CuNi or Al
Jacket prevents them from fragmenting

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36
Q

List the wounding mechanism of a bullet

A

Direct laceration (permanent cavity)
Temporary cavity
This either causes a wide haemorrhage zone or rupture of a dense organ like the liver
Shockwaves may rupture gas-filled organ
Secondary projectiles (e.g. bone)
Discharge gases at contact range will also cause damage

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37
Q

How far does the flame reach after a gun is fired

A

Around 3 inches

Can leave burn/singe marks at entry wound if within range

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38
Q

How far does the smoke reach after a gun is fired

A

Around 6 inches

Will leave soot deposition at entry wound if within range

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39
Q

Describe the formation of the temporary cavity in a gunshot wound

A

The huge pressure of the bullet causes a cavity to form behind the bullet
This can be up to 30-40x greater in diameter than the bullet
It only lasts milliseconds and then collapses in a pulsatile fashion
This pulsing causes lots of haemorrhage

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40
Q

What are the effects of the temporary cavity in a gunshot wound

A

Can cause a wide zone of haemorrhage around the permanent cavity or rupture dense, inelastic organs like the liver

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41
Q

What features may you find on the skin after a shooting

A 
Muzzle imprint - contact
Singeing due to hot gases - close range
Smudging of soot - within 6 inches 
Tattooing due to the propellent - scattered abrasions 
Skin defect from bullet 
Abrasions on the margins 
Microtears in HV shootings
Bullet wipe
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42
Q

What is powder tattooing

A

Skin injury caused by unburnt or partially burnt propellant grains
Forms individual reddish-brown punctate abrasions where grains hit
May or may not have rim of bruising (vital reaction)

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43
Q

What determines the spread of tattooing from a gunshot

A

Depends on powder, range, barrel

Pattern also depends on angle of entry - eccentric if angled

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44
Q

What is considered a near contact range

A

Within a few centimeters of target but less than intermediate

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45
Q

List the features of a contact range gunshot wound

A

Singeing of the entry wound from flame
Soot and propellant seared into margins
If there was loose contact then soot-laden gas will escape sideways
If the contact was angled then there will be an eccentric soot stain

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46
Q

List the features of a near contact range gunshot wound

A

Soot and propellant still seared into margins of wound
No tattooing - too close
Peripheral ring of soot staining - can be wiped off
Soot reaches 20-30 cm

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47
Q

What is considered an intermediate range shooting

A

Few cm to 1 m
Basically within arm’s reach
May still be suicide

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48
Q

What are the features of an intermediate range shooting

A

Powder tattooing - small, individual abrasions from the propellent
This cannot be wiped off like the soot
May have some associated bruising

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49
Q

What is considered a distant range shooting

A

Beyond 1m

Beyond arms length

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50
Q

What are the features of an distance range shooting

A

No flame or soot effect and no tattooing as too far away
Bullet is on its own which causes skin defect (hole) with marginal abrasion
Hard to estimate distance at this point

51
Q

How does angle affect shape of entry wound

A

Circular if impacting at right angle

Elliptical if impacting at another angle

52
Q

List the features of a bullet entry wound

A

Circular defect
Diameter is less than the bullet due to stretching of skin (will shrink back)
Abraded margin
May have soot or propellant in/around wound if close range

53
Q

List the features of a bullet exit wound

A 
Irregular shape
Diameter is greater than the bullet and larger than the entry wound
No abrasion (unless shored)
54
Q

Where is gunshot residue found on the hand

A

Deposited on radial side of firing hand

55
Q

How do you sample for GSR

A

Cotton tipped swab moistened with HCl
or HNO3 (or tape)
Put it through mass spec
This picks up the residue and tells you if they have fired a gun recently

56
Q

What is GSR composed of

A

Spheroidal particles of barium, lead & antimony compounds from primer
Caused by condensation and solidification of molten and vaporized primer and bullet materials

57
Q

How is gunshot residue forms

A

The firing pin strikes the primer which causes it to explode and ignited the gunpowder
Some unburnt gunpowder and vaporized components from the primer are found in the resulting gas
The gas causes a rise in pressure which ejects the bullet
The vapors quickly condense into spherical particles which can be deposited on the shooter
These particles are composed of one, two or three of the primer elements and it is these particles together with their morphology that make GSR unique - can be analyzed and matched

58
Q

How are ballistics tests carried out

A

The gun is fired into a water tank
The bullet is retrieved and can be analysed for rifling marks etc.
Firing pin can leave a mark on the base plate of the cartridge which can be identified

59
Q

Military weapons are designed to have their projectiles fragment - true or false

A

False
They are designed to not fragment so that they keep going whilst injuring as many as possible
They will exit the body

60
Q

What is meant by fully automatic fire

A

As long as trigger as pressed the gun will continuously fire until it runs out

61
Q

Where would you typically find the magazine of a gun

A

Usually found in the handle

62
Q

How do guns autoload

A

Once fired the gun ejects the spent cartridge and loads a new one
On a Glock the top slides back and forth to load and eject cartridge

63
Q

What are hollow point and soft point bullets designed to do

A

They are designed to mushroom on impact so that they stay in the target
Shouldn’t exit the body
Designed for hunting

64
Q

What are jacketed bullets designed to do

A

They are designed not fragment on impact

This allows you to hit more targets - designed for military use

65
Q

Which type of ammunition is larger - handgun or rifle

A

Rifle ammunition is much larger volume wise, bullet is same size
It contains more propellent so travels further

66
Q

Why does rifle ammunition travel further

A

Contains more propellent (larger ammunition)
This allows the bullet to travel faster and further
The longer barrel allows for accuracy

67
Q

What causes abrasion at the entry wound

A

Imprint abrasion at point of contact due to compression by nose of bullet
It compresses and stretches the skin before breaking it
Skin then folds inwards

68
Q

What distance does the WAD travel after a shotgun discharge

A

Around 1m or 3ft

Can be cardboard or plastic

69
Q

Satellite holes would occur at what distance after a shotgun discharge

A

Around 2m

Centre wound with a few smaller satellite holes as the pellets start to spread out

70
Q

Uniform peppering would occur at what distance after a shotgun discharge

A

Around 10m
Pellets can spread out and cause several wounds
Likely no central hole

71
Q

List the main types of shotgun

A

Single shot
Double barrel - side by side or over and under, fires 2 shots at once
Over & under
Bolt action
Lever action
Pump action
Auto-loading - military and police typically

72
Q

List the features of a shotgun

A

Smooth barrel
Fired from shoulder
Fires multiple pellets/lead shot

73
Q

What is the shotgun gauge

A

The number of balls of lead exactly fitting the barrel (same diameter) which make up 1lb in weight

74
Q

Describe the structure of shotgun ammunition

A

Base is a brass head plate
Above is the primer then the powder/propellent
The WAD (cardboard or plastic) sits on top of propellent
Modern guns may use plastic power piston instead of WAD
The shot/projectiles are above
All encased in a crimped plastic tube (rather than metal seen in handguns)

75
Q

What is the function of the ‘choke’ of the barrel

A

This is the taper towards the muzzle - decreases in diameter towards the end
It keeps the shot more closely clustered- channels the pellets closer together

76
Q

How do you measure the choke of a shotgun barrel

A

Measured as % shot striking within a 30 inch target circle at range of 40 yards
e.g. a full choke is 60% and a normal cylinder is 30% (same diameter all the way down)

77
Q

What is the function of the shotgun power piston

A

It pushes the shot out of the barrel but also exits and contributes to the wound
More effective way of channeling the explosive force from propellent
More complex mechanism than traditional WAD - made of plastic and double cupped (upper cup made of petals

78
Q

Describe the structure of the shotgun power piston in different guns

A

12 gauge, 16g & 20g have 4 petals
.410 has 3 petals
The petals are closed initially but open up and fall to the sides as fired
The power piston can indicate manufacturer & gauge

79
Q

At what distance does the shotgun power piston contribute to the wound itself

A

Below the range of 20ft

It will also strike the body at this range

80
Q

Describe the appearance of the shotgun power piston at different distances after firing

A

< 1ft, not yet opened nand will hit body
1-3ft, petals are starting to open and will leave abrasions when they hit
> 3ft, petals folded back and no longer get petal marks
> 8-10ft, strikes of to the side of entry wound
The power piston can indicate manufacturer & gauge

81
Q

What are the features of a contact shotgun wound to the head

A

Scalp laceration - hard to construct dimensions of weapon as so massive
Skull fracture - caused by huge energy
Brain may be “blown out” - caused by release of gas
Most pellets & wad may exit
Very mutilating injury due to gas and energy of the shot

82
Q

What are the features of a contact shotgun wound to the torso

A

Circular entry wound that matches muzzle diameter
Muzzle imprint
Soot smudging - loose contact
Burning or melting of clothes
Cherry pink wound margin due to carbon monoxide

83
Q

What are the features of a shotgun wound from various known distances

A

Below 2ft there is a circular wound matching barrel diameter
Tattooing present up to 3ft but no further
Scalloped margins by 3ft
Satellite holes (fliers) form by 4ft as individual pellets start to spread and central hole gets smaller
Cuff of satellite holes by 6ft - definite shape

84
Q

How can you estimate the distance of a shotgun from the wound if it was over 10 away

A

This would require test firing of the suspect weapon

This is because over 10ft the entry wound will vary with the range, length, choke of barrel and the ammunition

85
Q

At what distance would you get tattooing from a shotgun

A

Up to 60cm or 24 inches

86
Q

At what distance would you get smoke/soot on the body from a shotgun

A

Up to 38cm or 15 inches

87
Q

At what distance would you get burns on the body from the flame of a shotgun

A

Up to 15cm or 6 inches

88
Q

List signs of suicide by gunshot

A

Contact wound
high velocity blood spatter on steadying hand - blow back from the injury
GS residues on firing hand -hands should be swabbed
Evidence of test firing

89
Q

Which sex is more likely to commit suicide by gunshot

A

Males - more likely to use violent methods

It is rare in women (poisoning more common)

90
Q

List the most common sites for gunshot suicides

A

Head - 80% of cases
Typically the temple, forehead, mouth or chin
15% of cases are in the chest
5% in the abdomen

91
Q

What signs should be looked for on the hands of a gunshot case at autopsy

A

Look for soot, blood or residues (e.g. GSR)

92
Q

What are some of the issues at autopsy in gunshot cases

A

Shored or Partial exit wound - can be confusing
Bullet ricochet outwith & within body
Separation of bullet jacket & core - seperate wound tracks
Projectiles may embolise or move
Plastic wad and Al jacket invisible on X-ray
X-ray may magnify projectiles
Snooker ball effect of pellets - bounce off each other and spread around (messes up distance analysis)

93
Q

What is the function of the WAD

A

Cardboard or plastic disk that pushes the shots out of the barrel
It also holds them in place before firing
Will also leave the barrel

94
Q

How does range affect the spread of the bullets

A

The longer the range the greater the spread of pellets
Contact/close range typically a single hole
Start splitting at around 2 metres

95
Q

Describe the appearance of a contact shotgun wound

A

Circular hole wound with a surrounding ring of burns

96
Q

Describe the appearance of a close shotgun wound (few cms)

A

Circular entry wound with soot staining around it from the smoke

97
Q

What is a single shotgun projectile called

A

A slug

98
Q

Describe the appearance of high velocity blood splatter

A

At high velocity the blood sprays out in a fine mist

At lower velocities the drops will be larger

99
Q

You always X-ray a gunshot victim - true or false

A

True

Allows you to locate and retrieve projectiles (bullet, pellets etc)

100
Q

Why is the clothing of a gunshot victim retained

A

So it can be analysed and tested for things like GSR or blood splatter

101
Q

Are the individual rifling marks that are specific to one specific gun always the same for that gun

A 
No 
They are due to wear and tear in the gun and so  they will change over the years within the same gun 
Just because 10 years ago that specific rifling mark was made by that gun doesn't mean it will make the same marks today 
Its class characteristic rifling marks will be the same though
102
Q

Are handguns rifled

A

Yes

103
Q

What is meant by autoloading in hand guns

A

That you press the trigger each time and the gun will reloaded the next bullet automatically

104
Q

Are revolvers autoloading

A

No

Each time you must pull back a lever to reload

105
Q

What’s the difference between a shotgun and a rifle

A

A rifle has a rifled barrel that fires single rifle ammunition

A shotgun has a smooth barrel and fires multiple lead projectiles (balls bearing)

106
Q

How far does the propellant reach from a gun fired

A

18 inches

107
Q

When do discharge gases in particular cause a lot of damage

A

Especially in close contact with shotguns as gets lots of CO released

108
Q

how far does the propellant reach from a gun fired

A

18 inches

109
Q

If a gun is fired from more than 18 inches away what do you see on the body

A

Just the bullet entry wound

Everything else doesn’t reach far enough

110
Q

How can you tell from bone which side the bullet exited through

A

The wound will be larger on the side of the bone it exited through
Creates an outward cone shape

111
Q

What does a bullet do to the skin as it exits

A

It rips through it so the skin will fold outwards

There will be no imprint abrasion as seen at entry wound

112
Q

How can you tell an entry and exit wound apart

A

Entry - skin folds inwards and there is imprint abrasion
- the bone hole will be larger in the innermost side of that bone

Exit - skin rips outwards and no imprint abrasion
Bone hole is larger on the outermost surface of that bone

113
Q

What causes the muzzle imprint in contact shooting

A

It’s not a direct imprint abrasion from the muzzle itself but is in fact caused by the gas from the firing going into the skin and blowing it back into the gun muzzle

114
Q

What is bullet wiping

A

This is when the barrel of the gun hasn’t been cleaned so there is oil, dirt and grease that can be seen in the edges of the bullet track
Wipes off the bullet as it travels

115
Q

How can you tell apart a hard contact shooting and a loose contact shooting

A

If hard contact - entry hole is burnt with soot and propellent seared into the edges

Loose contact - The entry hole is still burnt but some soot will escaped outwards to side and will line the hole

116
Q

What must you be careful of when examining near contact gunshot wounds

A

The soot ring identifies it as near contact and the soot can be wiped off - may lose evidence if not documented

117
Q

What firing distances can be a suicide

A 
contact ( on skin)
near contact ( up to about 6 inches)
intermediate (up to 1 meter to 18 inches)
118
Q

What is shoring of exit wounds

A

When there is an abrasion around the exit wound (where there shouldn’t be)
This can occur if the skin was pressed up against a bra or a wall etc.

119
Q

What is a near exit wound

A

When the bullet ahs run out of energy and because the skin is stretchy and elastic it hasn’t quite been able to break through
You see a bruise and can feel the bullet underneath

120
Q

What does a contact entry wound between the eyes suggest

A

Most commonly suicide

Assassination

121
Q

What must you not do when removing a bullet from a near exit wound

A

Do not used toothed forceps as this could ruin the rifle markings

122
Q

If you have a case where the same bullet has entered/exited more than once (e.g. through arm then through chest) what does it suggest

A

High velocity rifle with a jacketed bullet

123
Q

What can cause the skin to split around a bullet wound

A

The high velocity gases

Forensic Medicine (13 decks)

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