Topic 9 - Terminal Ballistics (1) (Wound Cavities (Permanent Wound Cavity…
Topic 9 - Terminal Ballistics (1)
The study of how a projectile behaves when it hits a target and transfers its kinetic energy to the target.
Damage comes from the energy the bullet carries and the design of it. Evidence can spread over a wide area. Shooting at close range leaves distinctive marks. Energy is important HOWEVER is a small aspect, other contributing factors: material type, tumbling, the target.
Burns from hot powder residue. Pattern and spread gives distance from the weapon. Powder residue may be embedded and recoverable from the skin around the wound. Distribution and shape of pattern gives indication of incident angle. Easily mistaken from shotgun wounds.
Gas Injection Trauma
Star shaped (stellate) splitting caused by discharge gas injection between dermis and skull. Pattern characteristic of
contact gas injection
. Only occurs when bone is close to surface of the skin. Little tattooing indicates muzzle pressed against head.
Gun pressed against skin. Manufacturer markings may be evident around the wound. Contact wounds will always exhibit some kind of lesion (bruise).
If not human tissue, remove whole item that may contain GSR or a large section if possible.
Patterns (we can produce by using dyes that stain) are as important as the chemical composition. Samples should be taken before staining. GSR can precipitate or particulate.
Useful up to a couple of metre but after that the distance is too far for GSR to be present on target.
GSR remains of bullets. This will deposit on surfaces that the bullet contacts. Bullet leaves "wipe ring" at entry point. No on scene analysis, perform in laboratory.
Can be analysed for any firearm or ammo. Patterns should be consistent for a given firearm or ammo at the same distance. Conditions should be replicated for a high accuracy method. With ammo, different makers use diff propellant types, physical dimensions maybe be identical but can still produce different results, thus ammo identification is crucial.
Testing to find fire range but reproducing the same pattern. If possible use suspect firearm or one that is the same make and model. Use same ammo, if possible same batch as suspect ammo. Test fire onto sterile 0.5mm card. Range should be 0-2 m in 5cm intervals.
Preliminary test, chemical test detects the presence of
organic nitrite compounds
. Used to test for traces of explosive materials and propellants. However can give
thus not a conclusive test for GSR.
0.2% napthylenediamine dihydrochloride
2% sulphanilamide in 5% phosphoric acid.
Sodium Rhodizonate Test
Preliminary test but more conclusive. Metal deposition test which indicates the presence of lead. Performed after the Greiss test, spray 1% solution of reagents in distilled water onto test surface. Produces a red/pink stain indicating
of lead. Then treat with HCl, if stain turns blue then the presence of lead is
. Positive test of this plus positive Greiss test is strong evidence that a firearm has been fired.
Long range wounds
No muzzle imprint
minimal or no GSR
no gas injection trauma
no residue makes it nearly impossible to determine shooting range.
sonic and echo data can indicate position of shot.
penetration data CANNOT be used as is too dependent on impact site.
multiple entry wounds depending on shot type
no exit wound unless v close range
wadding may be embedded or mark the skin
up to 25m cartridge wadding may be embedded.
: reducing a square edge to a sloping edge.
sometimes only way to determine entry and exit wounds.
shape of hole can indicate the angle of impact. Key-holing is from acute angle impact and circular is from perpendicular impact.
: acute angle impacts skull and is
deflected within the cranial cavity
. Comminuted fracture will be directly opposite the point of entry.
: human bone is resistant to bullet damage. Smaller bones shatter, larger bones will chip and bullet will deform (can be deflected). Bullet may shatter, but if jacketed it may drop its core. Unjacketed bullets have a lower velocity so tend not to shatter but will deform easily. Fragmented bullets can make determining entry and exit points difficult. Deflected bullets may leave and re-enter the body again confusing the issue.
Soft Tissue Impact
High velocity bullets tend to over penetrate flesh at close to medium ranges (25-300m). This depends on structure of bullets e.g. hollow point bullets don't tend to fully penetrate as the "mushroom".
Polycarbonate rods can be placed into the permanent wound cavity to follow the path of the bullet.
Permanent Wound Cavity:
path of tissue destroyed by the transit of the bullet, formed by crushing the soft tissue or by tearing from shrapnel/broken bullets.
does not close up
size is NOT related to muzzle velocity, more so
tissue destroyed must be cut out to avoid death of cells (necrosis) and to encourage healing.
Temporary Wound Cavity:
cavity opened by the transit of the bullet through the soft tissue.
tissue will be damaged slightly but the natural elasticity will cause cavity to close immediately after passage of bullet
be proportional to bullet velocity.
bullet pushes the tissue out of the way forcing the tissues open radially, and the more elastic the tissue is the larger the cavity.
cavity is formed by bullet transmitting radial acceleration to the tissue, forcing it out laterally during penetration.
the kinetic energy passed into the moving elastic tissue is transformed into strain energy (as elastic potential energy).
cavity growth stops as it reaches its maximum diameter, strain energy is released causing return to its normal position along permanent wound cavity.
Low velocity, Large Caliber:
pistols, unjacketed or semi-jacketed
small permanent cavity, diameter of bullet
temporary cavity is cylindrical and regular, does not extend far beyond permanent cavity.
bullet loses energy quickly so remains in body.
High Velocity, Small Caliber:
rifle, always jacketed
large irregular permanent cavity if broken up
large temp cavity
bone impact will damage/fragment the round
non-partitioned bullets will tend to strip to core, then core may over penetrate (exit body) and jacket remains in victim.
Shot placement is more important than projectile power, size, or density.
Tumbling can be deliberately induced by having bullets with centre of gravity off axis. Designed to avoid direct wound tracks and cause extensive secondary damage. Discontinued.