By Christopher I’Anson
Director at ML services and training Ltd
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Physics of trauma
Causes of death in gunshot wounds (GSWs)
Weaponology
 Rifles
 Handguns
 Bullet design
 Shotguns
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There are several different types of energy:
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Kinetic
Thermal
Gravitational Potential Energy
Chemical
Elastic
Magnetic
Light
Sound
Electrical
(Nuclear)
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Each for is important
Energy can not be created or destroyed
 Therefore it dissipates into other forms
▪ This is what causes injury
▪ Bullets transfer kinetic energy into different forms which
cause damage
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This is the energy
exchange that occurs
when a bullet is fire from
a weapon
Chemcial
(Gunpowder)
Kinetic
(as bullet is propelled
outwards)
BULLET HITS TARGET
•Thermal
•Kinetic
•Sound
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Kinetic energy is the most common form of energy
found in trauma.
Kinetic Energy= ½ mass x velocity
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If we look at the example of the bullet again, half
the mass of the bullet times its speed is equal to the
amount of kinetic energy it has and there for the
amount of damage it will inflict.
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Hence a small slower speed projectile like a shotgun pellet
does not do as much damage on a target as a larger 50
calibre bullet from a high powered rifle.
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This must be considered when treating a patient who has
been hit by such projectiles.
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Projectiles are difficult to predict in terms for the
damage they cause for a number of reasons:
 the power of the weapon
 item producing the projectiles is not always known
 they may do any of the following:
CAVITATION
FRAGMENTATION
RICOCHET
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Cavitation is where the projectile forms a cavity or hole after
penetrating tissue. There are two types of cavity formed,
TEMPORARY and PERMINANT.
 A temporary cavity, as the name suggests, is a cavity the is formed by
a projectile as it passes through an object but does not remain after
that object has passed.
 The permanent cavity is the cavity that remains after the projectile is
no longer acting on the body.
▪ The greater the velocity and mass of bullet the greater the cavity size
▪ 7.62 rifle > hand gun
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The picture on the left is a diagram of cavity formation. Here you can see the
temporary cavities marked by blue arrows, the black indicates the direction of
the bullet, the red arrows show the permanent cavities. The picture the right is a
picture of some ballistic gel as a bullet passes through it. The best (and most
interest) way to view this is by looking at examples on YouTube.
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The size of the permanent cavity and the
wounding depends on:
 Bullet size
 Bullet weight
 Bullet design
 Bullet Speed
 Tissue damaged
 Depth of penetration
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Fragmentation is where the projectile disintegrates resulting in more
than one piece of projectile acting on the body.
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These can result in unpredictable damage to the body and the fragments
may continue to have velocity and travel through tissue after
fragmentation has occurred.
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Fragments of bone can also cause fragmentation injury and act as
secondary projectiles.
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5.56mm bullets (e.g. SA8O) cause most of their damage by
fragmentation.
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Ricochet is where the projectile deflects and
alters its path
 this again means that the path and damage is not
easily predicted
▪ however the presence of an exit wound may help detect
if this has occurred and the potential damage that may
have occurred.
▪ NB: just because there are two holes does not mean
that there is an entry and exit
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You should ask:
 What weapon was used
 Type of shot (bird, hollow-points etc.)
 Number of gunshots herd
 Proximity of shot
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Every victim of a gunshot wound has an entry wound
 The size of this depends on the weapon used
 They may have an exit wound but not necessarily
 The presence of two wounds does not always mean one is an exit
wound and the other an entry
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The presence of an exit wound depends on a number of
factors
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The exit will always be larger than the entry wound
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The location/ presence of an exit wound will depend
on:
 Ricochet inside the body
 Type of round
▪ Hollow-points and half jackets are less likely to have one
▪ Shot guns using bird shot at a standard range are unlikely to have
exit wounds
 Velocity of round
 Position of the patient
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If patient B was hit by a rifle
bullet then you would expect
the bullet to enter the front
of the chest and exit near
the shoulder blade
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If patient A was hit in the
same part of his chest as B it
A
B
would exit lower down as he
is bent over
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Tissue destruction
 Less come COD
▪ The body only needs a small about of tissue to survive i.e. the brain stem
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Bleeding (most common COD)
 Decreased blood pressure
 Loss of consciousness
 Vomiting
 Airway compromise
 Capillary pressure is less than intra-cranial pressure causing cerebral
vessels to collapse
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By Christopher I’Anson
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Rifles come in different sizes with different
calibre rounds (diameter of round)
 Range from 50 cal to 5.56 cal
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The larger the calibre the heavier to bullet
The heavier the bullet the more energy is
transferred into the target
The more energy transfer the more damage
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Rifles are the most powerful type of gun at
medium-long range and therefore most
deadly (shotguns at close range are more
deadly)
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Rifle name
Calibre (mm)
Weight of bullet
(grains)
Speed of bullet
(m/sec)
AK 47
7.62
126-176
850
SLR
7.62
SA8O
5.56
AK74
5.45
-------55-62
-------900
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Table 1: This table shows the details of
different weapons and their bullet
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The AK47 and SLR have a large calibre round
and cause the most damage
 They have a large permanent cavity
 Their bullets tumble as they loss velocity
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The round from the standard British armed forces
rifle is the fastest in the table
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It does its damage by fragmentation
 This maximises the size of the permanent cavity
 Fragmentation occurs after the bullet hits the target
 It may occur after the bullet exits the target
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Handguns account for 70% of GSWs in the
USA
They are 1/10th as powerful as rifles
They have two mechanism of injury (MOI):
1. Crush mechanism (permanent cavity): this is
the hole the bullet makes as it passes through
tissue
2. Stretch mechanism (temporary cavity)
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The MOI are similar to that of a rifle
 However there is very little stretch damage and a
small temporary cavity unlike a rifle
 Therefore most of the damage is done via the
crush mechanism
▪ This makes handguns less effective at stopping people
▪ Victims can continue attacking or run away after
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Handguns have a lower velocity
 They are less likely to have an exit wound
 There damage/ stopping power comes from direct
injury to vital organs such as the brain, heart or
liver
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Here you can see the
comparison between the
cavities a rifle makes (A)
and that of a pistol (B)
A
 NB: the rifle bullet has also
fragmented unlike the
pistol
B
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Bullet designs for rifles and handguns vary
 Full metal jacket: fully encased in metal with lead
 Half jackets: exposed lead tip to allow the bullet
mushroom out on impact (bottom right)
 Hollow-points (bottom left): similar to half jackets
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Shotguns use cartridges that contain multiple
pieces of shot.
 Can be up to 200 small balls (bird shot)
▪ Can be glued to getter to make a slug which is deadly
 Larger shards (buck shot)
▪ For large animals
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This is an x-ray of a
patient who way shot
with birdshot
 You can see multiple small
pellets
 The spread shows the shot
was at medium range
 The shots are only
superficial with minimal
damage
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Energy always transfers into other forms
 This causes damage
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Many types of weapon and shot
 Varies the type and severity of injury
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Bullet trauma is multi-factorial
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