Physical Methods Exam 3

Firearms identification

determines if a bullet was fired from a particular weapon

Ballistics

Study of the projectile itself

Two groups of firearms

Handgun and Shoulder fire guns

Two types of firearm barrels

smooth and rifled bores

Rifling

Adds spin to the projectile for increased accuracy

Lands (on bullet)

Raised areas caused by indentations on bore

Grooves (on bullet)

Indentations caused by raised areas on bore

Caliber

Internal diameter of the barrel

How to measure the diameter of the bore

Measure from land to land

Gauge

Diameter of shotgun bore specifically

Class Characteristics of gun

Land and groove number, width, and direction of twist

Individual characteristics of gun

Striation markings and minute imperfections

What two things do bullets have that make them different from ammunition

Parabolic front and wind splitting shape

What are two types of ammunition

Cartridges and shotgun shells

Internal ballistics

Events within the firearm

External ballistics

Events between bullet leaving barrel and striking target

Terminal ballistics

Events when bullet strikes target

The firing pin strikes the… and ignites the…

strikes the primer and ignites the powder

After the firing pin strikes, the expanding gases propel…

Propel the bullet forward and the case/shell against the breechblock (back)

How does the cartridge case/ shell case get impression markings

Through contact with the metal surfaces passing through the barrel

What percentage of recivered firearms have removed serial numbers

15%

What type of material does Magnaflux Method work on

Magnetic metals

Explain Magnaflux Method

Nondestructive, mixture of fine iron fillings and and light oil is applied while placing a magnet on the other side, fillings arrange themselves in the oil to provide a shadow of the original number

What type of material does acid etching work on

Materials with both magnetic and nonmagnetic material

Explain the Acid Etching Method

Slow and destructive. Pretreatment with grinding tool then reagent is applied and dissolves metal to show numbers

How to preserve and collect a gun

Unload gun and clear for removal. If ammunition was removed not number and type, if revolver, make diagram of barrels, then put in gun box and fix with zip ties

Collection and Preservation of Ammunition

Individually pack each bullet and cartridge case in paper envelope and remove bullets from walls with rubber or plastic objects

How to examine bullet in lab

Look for rifliong characteristics such as lands and grooves, caliber, and direction of twist.

How to compare bullets

Use comparison microscope to compare with a bullet shot in a water tank, and find matching striations or determine no match

What kind of characteristic do cartridges give

Class characteristics (caliber, location, size, shape of weapons firing pin, sizes of extractors and injectors), and individual (Specific imprint of firing pin)

What databases are used

Integrated Ballistics Identification System (IBIS) and National Integrated Ballistics Information Network (NIBIN)

Ghost gun

Gun with 3D printed parts

What locations does GSR analysis include

Places on the skin and clothing and surfaces

Components of GSR

Primer, propellant/gunpowder, barrel scrapings, metal from projectile

Components of primer

Initiator (mostly lead styphnate), Oxidizer (barium nitrate- keeps things burning), Fuel (antimony sulfide- starts burning), Sensitizing (TNT)

Propellant/ gunpowder types

Black powder (lots of soot and carbon and potassium nitrate), and smokeless powder (nitrocellulose and nitroglycerine)

What is single base vs double base

single: nitrocellulose

double: nitrocellulose and nitroglycerine

Core of bullet components

lead and antimony/ lead and tin

jacket of bullet components

copper alloy w/ Zinc or tin

What are the two types of detectable gsr

organic and inorganic

What are the most and least common locations for gsr

hands and clothing (least= hair face and other people)

is gsr fragile? How long does it last

very. around 3 hrs

what is used to prevent the loss of gsr on hands

hand bag

how to package clothes with gsr

package individually, fold with as little folds/ wrinkles as possible, put in paper bag

route of swabbing on hand

tip of pointer finger, around web of hand, to thumb tip

types of gsr collection

swab w/ nitric acid (most common), aluminum stubbing

Color test for gun residue

modified greiss test

Color test for lead residue

Rhodizonic acid test or dithiooxamide acid test

How does modified griess test work (include color change)

put evidence on DESENSITIZED photo paper and iron with dilute acetic acid. Nitrites= rosy orange

Rhodizonic Test color change

Lead= violet

Dithiooxamide test process and color change

Press paper with ammonium hydroxide onto evidence then add dithiooxamide solution on there. Copper/metal= greenish black/ dark green

Methods used to detect primer residues

Atomic Absorption Spectroscopy, SEM-EDX

What type of sampling is used for Atomic Absorption Spec

Nitric acid swabbing

Flaws of Atomic Absorption Spectroscopy

1 metal at a time and tedious

What type of swabbing used for SEM EDX

Aluminum stubbing

Cons of SEM-EDX

Expensive