firearms final

what types of things are looked at regarding fired bullets- the examination process usually includes the following observations and determinations:

● Bullet weight

● Composition of the bullet

● Base description

● Type and position of cannelures

● Manufacturer/marketer

● General rifling characteristics

·      Caliber

·      Number of land and groove

·      Direction of twist

bullet types

full metal, total metal, hollow point

full metal

encloses the entire bullet, with the exception of the base.

total metal

fully encloses a bullet core

hollow point

has a hollow tip, and it expands on impact- mushrooming

Why LEO uses them

·      They use it today because its more lethal due to its expansion and its safer to people around

General rifling characteristics examples

o   Caliber, number of lands and grooves, direction of twist, land and groove impression dimensions

general rifling characteristics

are gross impressions visible to the naked eye are made in the surface of bullets while in hard contact with the bore of the barrel.

trace evidence found on fired bullets

blood, hair, fibers, glass, paint, bone, soft tissue, wood, metal smears, masonry, stone

Instrumentation used for measuring bullet diameter / width

vernier caliper

types of cannelures

knurled, smooth

what is a cannelure

·      They are very useful in determining the manufacturer and, in some cases, the stock number of bullets that are only used only for specific purposes.

GSR

·      composed of primer residues from the combustion of the cartridge priming mixture when the primer was struck by the firing pin

o   Residues resulting from the burning of the propellant

o   Material generated by the interaction of the bullet within the inside of the barrel

o   Unburned and partially burned powder

chemical testing

o   Modified griess test for nitrite compounds, a product of burning a nitrate, such as a smokelss powder, or reverse modified friess test

o   Dithiooxamide test- for cuprous materials

o   Sodium rhodizonate test – all forms of lead residues or bashinski transfer technique

distance determination

performance of gunshot residue analyses that compare with a known distance test fire of residue patterns

environmental challenges with GSR

o   Wet weather conditions can degrade the amount of water soluble nitrite residues present.

o   Extended exposure to high temp and humidity degrade nitrite residues

o   Extended exposure of a body to the outdoors may eliminate nitrite residues

determining entry/ exit

smooth, beveled

smooth

entry- tends to be smaller

beveled

exit - tends to be larger

concentric striations

circular fracturing around hole

radial cracks

·      form at right angles to the bullet hole

o   Tell you what came first

o   Sequence of impacts; radial cracks stop at pre existing cracks

Field test kit to swab bullet holes

BTK test kit

Reconstruction methods

stringing, laser + tripods, trajectory rods

The big question we ask ourselves

Is this a homicide, suicide or accident

different methods of obliteration of serial numbers

drilling, engraving, grounding, peening/ punching, scratching, overstamping, overpunching, welding or other heating process

method of serial number restoration

polishing, light and alternate light sources, chemical etching, electrolytic chemical etching, magnetic particle inspection

incapacitation factors

location, velocity, caliber

temporary cavitiy

·      damages but may not destroy tissue within an area, stretched tissue may not ruin arteries or cause large blood loss as some tissue tolerate stretch

permanent cavity

hole in body part, must be sewn up

types of gunshot wounds

tight contact, close contact, close range, distance shot

billiard ball effect

pellets spread out after hitting eachother

Medical intervention – give ex looking at fired bullets removed from autopsy

-              When a bullet is recovered from a living victim, it may bear additional microscopic marks that are caused by the actions of medical staff providing care (forcep impressions on the bearing surface). These marks may alter or obliterate the marks that occurred during firing.

bullet

Nonspherical projectile for use in a rifled gun barrel

The examination process usually included the following observations and determinations

o   Bullet weight, composition of the bullet, base description, type and position of cannelures, manufacturer/ marketer, GRC, caliber, bullet design

major questions

o   is there primer residue on the victim, distance determination, scene details, location/ entry

-              responsibilities of a firearm examiner

o   firearm examination/ diagnostics/ operability testing

o   microscopic comparisons

o   serial number restoration

o   reports

o   testimony

o   NIBIN

o   Distance determination

o   GSR

o   Tool marks

Plastic deformation

permanent change in the shape or size of a solid body without fracture resulting from the application of a sustained stress beyond the elastic limit

-              Serial number applications

o   Roll stamped, impressed, pin stamped, dot matrix, and laser etched

Info found at autopsy

entry exit size, graze wounds, wound path, measured body area, internal injury, Xray, recovery of bullet