Gardner Chapter 12

Cartridge

the complete unit of un-fired ammunition

Cartridge case

the sub-unit of the cartridge that is expelled from the firearm under the pressure created by the burning propellant

Projectile/bullet

the sub-unit of the cartridge that holds the primer and propellant

Internal ballistics

the study and examination of the firearm itself

Who deals with internal ballistics?

firearm examiner

What three questions does internal ballistics try to answer?

Does the weapon operate as intended?
Can it operate at all?
Are there any aspects of the weapon capable of creating some form of accidental discharge?

Terminal ballistics

Consideration of the effect of the bullet on a human target and defining the path through the human

Who deals with terminal ballistics?

Forensic pathologists

close contact

the muzzle is in direct contact with the skin

loose contact

the muzzle is in extremely close proximity to the skin, but there is a small gap

near contact

the muzzle is no more than 5 inches from the skin

intermediate range

the muzzle is typically between 5-40 inches
deduced from stippling around the wound

Indeterminate range

no conclusion can be drawn

tangential wound

bullet skims the surface producing several shallow wounds

grazing wound

projectile leaves only a minor abrasion

External ballistics

considers the path and trajectory of the bullet after leaving the barrel of the weapon to its final impact

Who deals with external ballistics?

CSIs

penetrating defect

the bullet enters but does not exit a surface

perforating defect

the bullet enters a surface and exits

Ricochet or deflection

bullet strikes a surface and deflects off of it without penetrating surface completely

Tangential defect

bullet skims a surface, creating a series of defects

Calculating impact angle

impact angle is the inverse sin of minor axis divided by the major axis

__ defects tend to present an appearance of a cleanly punched hole

entry

__ defects tend to be more irregular and may have a coning effect or have material pushed away from the defect

exit

What are two additional indicators of direction of travel for metal impacts?

pinch point
wake effect

Pinch point

the point where the bullet and metal first meet
a small island of paint survives

Wake effect

small fracture lines in the paint and on occasion the metal itself

What are the three areas of study that make up ballistics?

internal, terminal, external

What are three ways the CSI might verify that a defect is associated to a bullet impact?

chemical evaluation, the presence of a bullet, the presence of bullet fragments

How effective are angle of impact determinations for bullet holes in solid substrates? Human skin?

Bullet holes in solid substrates are sufficiently accurate when using a stabilized rod. Raw positioning can affect the angle as much as 5-8 degrees.
Human skin has limited value as there could be deviations up to 20 degrees

Why is effective documentation of bullet defects so important?

Because defects can look the same (similar to bloodstains) and extra documentation needs to be done to avoid photography confusion problems. 

Describe the two basic angles that must be measured after inserting a trajectory rod into a bullet defect?

Horizontal Angle- the angle of the muzzle in relation to the target using a horizontal reference line. It shows movement right or left and is measured using a protractor aligned with a horizontal plane. 

Vertical Angle- the angle of the muzzle in relation to the target using a vertical reference line. It shows movement up or down and is measured using a protractor aligned with a vertical plane or the standard angle finger. 

What is meant by the Zone of Possibility when describing shooter positions?

Zone 1 - an area considered ‘most probable’, generally some point along the trajectory at or lower than the shooter's shoulder height and considered to be easily achieved given the specific context presented in the scene. 

Zone 2 - an area considered possible but awkward. Along the trajectory rod, higher than shoulder height. 

Zone 3 - an area impossible given the data. The shooter is physically unable to align the barrel and produce the trajectory.

What is the difference between a penetrating and perforating bullet defect?

penetrating- enters but does not exit

perforating- enters and exits the surface

When discussing a bullet defect in metal, what is a pinch point and how does it aid the CSI?

The pinch point is the point where the bullet and the metal fist meet. At this point, a small island of paint often survives. 

Indication of the directionality of the bullet

When discussing a bullet defect in metal, what is the wake effect and how does it aid the CSI?

Involves small fracture lines in the paint, and the on occasion in the metal itself, arcing out and away from the defect. The fracture lines extend out and opposite the direction of travel.