Criminalistics exam two

FRSC242.01

balistics

-the branch of physics that deals with the flight of projectiles

-the science of the passage of the projectile through the barrel of the gun, in flight and at the instant of the impact

what are the three major components of ballistics

internal, external and terminal (wound)

what are firearms class characteristics

-make of the firearm

-caliber/gauge of the firearm

-rifling pattern contained in the barrel of the firearm

-breech marks

-firing pin impressions

-extractor marks

-ejector marks

so in general its things that can be identified to a specific type or model of firearm

what are firearms individual characteristics and what are they caused by

they are unique marks produced by the random imperfections or irregularities of tool surfaces. produced incidental to manufacture and or caused by use, corrosion or damage

what are examples of individual characteristics of firearms as evidence

-number of lands and grooves

-diameter of lands and grooves

-width of lands and grooves

-depth of grooves

-direction of rifling twist

-pitch degree of twist

-angle of twist

handgun

firearm designed to be used with a one-handed grip

revolver

handgun that holds cartridges in a revolving or rotating cyclinder

semi automatics or pistol

a handgun that fires and reloads itself before firing another shot; a self loading handgun

single action

a handgun that is cocked by drawing back the hammer, either by the action of the trigger, or manually by the thumb

double action

pulling the trigger both cocks the hammer and fires the guntypically allowing for quicker shots without manual cocking.

be able to label the parts of a revolver

-front sight

-barrel

-cyclinder

-rear sight

-hammer

-cylinder release

-backstrap

-grip

-trigger

-trigger guard

-ejector rod

-muzzle

describe a revolver’s body

-standard cylinder

-solid frame with loading port

-top break action

be able to label the parts of a semi-automatic

-front sight

-barrel

-slide stop

-rear sight

-hammer

-safety

-grip

-magazine

-magazine release

-trigger

-disassembly lever

-slide

what is the first thing you do at a crime scene if you find a gun?

after photography. hit trigger and unload magazine, meaning you have released the magazine to remove majority of the live ammunition from the gun

how do you truly render a gun safe

take a gun apart but less render at crime scene, to render safe, magazine release, pull slide back to lock, and action will eject any remaining rounds/cartridges and look through and can see no shells or bullets

at a crime with guns, what do you account for

record how many live rounds/cartridges have been shot and how many remain. account for them all if you can

what does the red spot mean on a gun

that the safety is off

single shot pistol

-considered antique gun now

-really small

-one shot to get you out of trouble

describe illegal/modified weapons

-not meant to fire live rounds

-lowkey janky looking guns but as long as you have primer and activator with firing pin, it could shoot

rifle

a firearm having a rifle barrel and designed to be fired from the shoulder

shotgun

a smoothebore firearm designed to be fired from the shoulder; may ahve a rifled barrel

be able to label a rifle diagram

-stock (body)

-receiver (metal at top)

-ejection port (for discharged bullets)

-rear sight

-barrel

-front sight

-muzzle

-magazine

-trigger guard

-trigger

-safety

how is a rifle loaded

magazine fed

describe rifle mechanisms

lever action, discharged, the used cartridges cases are ejected and new live rounds enter the chamber

describe shotgun bolt action mechanism

pump ejects, then the magazine is reloaded and ready to fire

caliber

usually measures as the diameter of the bore from land to land to opposite land expressed in hundredth of an inch, thousands of an inch or millimeters

-sometimes given as the diameter of the bullet which is the distance between grooves

describe imperial measurements for caliber

for ex. “.22 caliber” or “.45 caliber” are imperial measurements designations. .22 and .45 is the diameter measured in inches

describe metric measurements for caliber

these are also common. for ex. a 9mm handgun has a bore diameter of ~9mm. -no decimal and drop the word caliber

explain why caliber isn’t exact math

-rarely exact numbers

-the difference between each round lies in the powder charges and cartridge length, not the size of the projectile they fire

-must use the recommended caliber per gun

guage

-the diameter designation for smooth barrel firearms or shotguns

-equal to the number of round lead balls of the diameter of the interior of the barrel required to weigh one pound

ex: 4,8,10,12,16,20 or 410 GUAGE

how to determine the caliber of a gun

-check the chamber or barrel, should be stamped there

-can also eject magazine and check there

how to measure caliber

distance between high points or lands

head stamp claiber/ guage can be found where

on the cap or end. you read what it says for the caliber

cartridge

in common usage, a complete round or combination of components including the case, primer, powder and projectiles

case

the component of the cartridge that contains the propellant; brass for pistol and rifle rounds, and plastic or cardboard for smooth bore rounds

handgun cartridges for case is three sections

-mouth

-body/powder

-base

describe rimmed vs rimless cartridges

the RIMMED goes straight down to base, the RIMLESS goes inward, for semiautomatic so they can snatch onto it and reload itself

.22 caliber ammunition

-small pellets inside

-even smaller projectile entering body and hitting in the right place is enough to cause fatal injury

rifle cartridge components

top to bottom is

-mouth

-neck

-shoulder

-body

-base

be able to identify the cartridge cases for both rifle and handguns

-primer

-powder

-wadding (cardbaord or plastic)

-holds projectile

-contained in case

at scenes with cartridges..

collect the casing and the wad because they are both unique identifiers

rifled/slug shots

just one piece of metal so no different than a bullet. it will travel, meant to go through, meant to do phsyical damage and stop the action

buckshot

multiple pieces, will spread out

-may go off to side and hit objects or others other than the action(target)

shotgun cartridge components

birdshot

buckshot

slug

whats in the shotgun cartridge case

-primer

-powder

-wad

-projectile

-case

powder

-a common term for the propellant

-powder=propellant

primer

a small metallic cap containing a detonation mixture, which when struck ignites the powder inside the case

gunpowder

has multiple versions of it

primer components

-anvil

-cup

-complete primer is anvil and cup with explosive

-looking at small yellow part in center. this is what you need to hit the start of the chain reaction

centerfire

any round that requires a centrally places primer in the base of the cartridge case to initiate combustion of the propellant

rimfire

a cartridge that does not have a centrally places independent primer, the primer compound coats the base of the inside of the cartridge case

similarities of centerfire and rimfire

-primer

-powder

-brass casing

-and bullet

projectile

the component of the cartridge that is fired from the barrel and eventually hits a target; in common usage, the bullet

shot or shotgun cartridges

small lead or steel balls that comprise the projectiles of a shotgun round

black talon and teflon were known as what

“copkillers” “amour piercing bullets”

rifling

the spiral cut on the internal surface of the barrel of a rifle or pistol, and some shotgun barrels

-on barrel or recovered discharged bullet

lands

the PROJECTING component of the rifling

grooves

the RECESSED component of the rifling

rate of twist

the distance the projectile needs to travel down the barrel to complete one full revolution

ex 1 turn in 12 inches

pitch

refers to the angle the rifling is cut in the barrel

laboratory examinations include what

-function testing

-bullet/projectile identification

-cartridge comparison

-shot and wadding identification

-shot patterns

-gunpowder patterns

-serial number restoration

gunshot residue testing

-scanning electron microscope/energy dispersive x-ray

-inductively coupled plasma spectrometry

stippling

-deposition of fragments of powder into the skin as a result of a gunshot wound of relatively close range

-abrasions caused by the impact of unburnt particles of powder impacting the skin

what is the primary concern of forensic firearm and tool mark examination

to ensure proper functionality and determine if a bullet, cartridge case or other ammunition was fired from a particular firearm

how do forernsic firearm/tool mark examiners do comparisons

comparison microscope

-two microscopes in one contraption, to compare knwon and questioned evidence

cartridge components

case: holds everything together. also has a seal to prevent gas leakage

bullet: top that actually comes out

primer: ignition source

propellant: powder charge

powder description

-propellant fuel of the cartridge

-deflagrates producing a large increase in gas pressure

-different shapes and sizes

primer description

-ignition system of the cartridge

-contains a small amount of explosive

caliber description

-diameter of the projectile or bore

-measured in hundredths of an inch or mm

-used to designate ammunition for rifled firearms

shotshell description

holds everything together with shell case

-birdshot

-buckshot

-slug

wads description

-separate contents of shotshell

-holds projectiles

firearm defintion from the talk

an assembly of a barrel and action from which a projectile is propelled by forces of combustion. the legal definition varies on jurisdiction

-is a tool

what are the three main types of guns (according to the talk)

-handguns/pistols/revolvers

-rifles

-shotguns

Handguns/pistols/revolver according to talk

-Designed to be fired with one hand

-Pistol: Chamber emptied and reloaded after each shot by mechanical force

-Revolver: cylinder rotates when cocked into position

rifles according to talk

-designed to be fired with two hands with rifled bore

-between rounds, grab bolt handle

shotguns according to talk

-designed to be fired with two hands with smooth bore

-fire multiple projectiles at once

-lower powered and harder to identify because of less pressure cartridge

actions

the target

action types

-single shot

-repeating

-semiautomatic

-fully automatic

describe single shot action type

break action fires one round

describe repeating action type

pump action, lever action, bolt action, revolver. between round stores undischarged rounds and needs action to get new rounds

describe semiautomatic action type

blowback

describe fully automatic action type

blowback

class characteristics of guns

determined prior to manufacture

-rifling

-diameter of bullet

-left or right twist

-firing pin shape: elliptical or circular

individual characteristic of guns

-by use or abuse

-use comparison microscope for this to see slight difference or agreement

where is a repeating firearm loaded from

the bottom

function testing categories

-operability

-test fire

-weight of trigger pull

-mechanical integrity (shock and drop)

impression for firearms

a harder object is forced into the surface of a softer object with no relative motion

ex: firing pin impression

striation

a harder object is scratched across the surface of a softer object

ex. rifling

four conclusions for firearm identification

-identification: tool marks produced by the same tool

-elimination: tool marks not produced by the same tool

-inconclusive: tool marks may or may not have been produced by the same tool

-not suitable for examination: not suitable due to mutilation or damage

serology

the scientific study of blood serum; usually referring to the diagnostic identification of antibodies in the serum; also used to describe a broad scope of lab tests that use specific antigen and serum antibody reactions

forensic serology

applications of immunological and biochemical methods to identify the presence of abody fluid or tissue sample encountered in connection with the investigation of a crime and the possible genetic characteriza of the sample with a view to determining likely donors thereof

blood

a highly complex mixture of cells, enzymes, proteins and inorganic substances; a slightly alkaine fluid made up of water, cells, enzymes, proteins and inorganic substances that circulate throughout the circulatory system

-human body contains ±10 pints of blood

components of blood

-plasma

-erythrocytes

-leukocytes

-serum

-antibodies

-antigen

describe the blood component: plasma

the fluid portion

-most fluid portion of blood consists of plasma, which is mostly water, and serum, which is yellowish and conhtains white cells and platelets

describe the blood component: erythrocytes

red blood cells

-the most NONfluid portion of blood consists of red cells, which outnumber white cells by 500:1 and are of most interest to forensic scientists

describe the blood component: leukocytes

white blood cells

-a colorless cell vthat circulates in the blood and body fluids and is involved in counteracting foreign substances and disease; a white (blood) cell

describe the blood component: serum

the liquid that separates from blood when a clot is formed

-an amber colored, protein rich liquid that separates out when blood coagulates

describe the blood component: antibodies

a protein that destroys or inactivates a specific antigen; basis for A-B-O blood typing

describe the blood component: antigens

a substance, usually a protein that stimulates the body to produce antibodies against it