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Analytical Techniques In Forensic Science > Forensic Ballistics > Flashcards

Forensic Ballistics Flashcards

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1
Q

What are the different types of guns?

A

-Self loading Pistol
- revolver
-Shotgun
-Rifle

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2
Q

What is the difference between rimfire and centerfire?

A

Rimfire refers to a firearm cartridge that has its priming compound located in a ‘rim’ around the base of the cartridge casing. Centerfire cartridges have an external pocket in the base where the primer is inserted.

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3
Q

What type of gun is a GFL 9mm Luger for?

A

Pistol

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4
Q

What type of gun is a Magtech .88 special-short for?

A

Revolver

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5
Q

What is the difference in ammunition for pistols and revolvers?

A

Pistol cartridges have a groove at the base that allows it to be ejected easily. Revolver cartridges have a larger base so that they are held in the cylinder.

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6
Q

What is the most common gauge for a shotgun?

A

12-gauge

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7
Q

What does calibre mean ?

A

It’s a unit of measure indicating the diameter of a gun barrel and the diameter of the gun’s ammunition

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8
Q

What is the bore?

A

The interior of the barrel of a firearm

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9
Q

What is the cartridge case?

A

It houses the bullet, primer and propellant

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10
Q

What is the primer?

A

The gun’s firing pin strikes the base of the cartridge and friction the cause ignition of the percussion primer

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11
Q

What is the propellant?

A

Chemicals that burn to create high pressure that forces projectile along barrel

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12
Q

After the primer has ignited the propellant what happens to the bullet?

A

hot gas is produced which expels the bullet

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13
Q

What is gun shot residue?

A

Any particle/ residue from the primer and propellant that are deposited on surfaces close to the gun

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14
Q

Why is primer residue more useful than propellant residue?

A

The chemical structure isn’t found in the general environment

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15
Q

What are the primary ways of acquiring gun shot residue?

A

-firing a gun
-Standing close to a gun when its fired

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16
Q

What are the secondary ways of acquiring gun shot residue ?

A

-handing a recently fired gun or spent cartridge case
-physical contact with someone who is contaminated

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17
Q

How much GSR is transferred each time it comes into contact with someone?

A

10%

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18
Q

How far does gunshot residue from a handgun travel ?

A

3m

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19
Q

What does primer gunshot residue contain?

A

Lead, barium, antimony and often other elements

20
Q

How is primer GSR analyzed?

A

SEM- highly magnified images and chemical analysis

21
Q

What does it mean for primer GSR to be highly characteristic ?

A

That it’s not produced by anything else other than guns/ firearms origin

22
Q

What are advantages of primer GSR?

A

-recovered from surfaces using adhesive tapes
-Does not chemically degrade

23
Q

What is the composition of primers?

A

-explosive
-oxidizer
-sensitizer
-frictionator
-fuel
-binders

24
Q

What is an oxidizer?

A

Produces oxygen to enable combustion

25
Q

What is a sensitizer?

A

Added to ammunition primers to make them more sensitive

26
Q

What is a frictonator?

A

Substance that increases the sensitivity of the primer mixture to reduce the chance of misfire

27
Q

What is the primer composition of sinoxyd ?

A

Lead Styphnate -explosive
Barium Nitrate- oxidizer
Lead Dioxide- oxidizer
Tetracene- sensitizer
Antimony Sulphide-fuel/frictionator
Calcium Silicide- fuel/frictionator

28
Q

How long does GSR stay on bags, windows and vehicles ?

A

Depends on circumstances and cleaning

29
Q

How long does GSR stay on clothing ?

A

Discarded clothing and pockets can be indefinite but clothing that is worn continuously up to 24 hours

30
Q

How long does GSR stay on hands, face and hair ?

A

Hands- up to 4 hours
Face - up to 6 hours
Hair- up to 12 hours

31
Q

What are types 1-3 of GSR ?

A

Type 1 - Lead, barium and antimony.
Type 2 - Lead, barium, antimony and aluminium.
Type 3 - Lead, barium, antimony and tin.

32
Q

How is the calibre of a 20-gauge shotgun defined ?

A

The diameter of a solid sphere of lead weighing 1/20th of a pound

33
Q

What are the different methods of detecting GSR ?

A

Bulk methods - colour tests
SEM

34
Q

Why are bulk methods unreliable ?

A

The elements are common in the environment and doesn’t tell you whether the elements are in one particle

35
Q

Why is SEM a better method of detection ?

A

-Analyses individual particles
-Distinguishes between different primers
-tells if the elements are in one particle

36
Q

Why is GSR often round ?

A

Formed under high pressure

37
Q

How are samples of GSR taken ?

A

-adhesive tapes mounted on aluminum stubs and carbon coated
-Now pre-prepared circular stubs more common

38
Q

What level of GSR is considered very high ?

A

> 50 particles

39
Q

Why are armed police officers likely to have GSR on their hands and clothing ?

A

As they carry firearms so they more likely to have high levels of GSR on them if they’ve recently fired their gun.

40
Q

Why can armed police officers potentially ruin the evidence of a case ?

A

If the reside is the same as crime ammunition it can be impossible to determine the source

41
Q

How must specimens in a SEM be ?

A

In a vacuum

42
Q

What is the primary electron in SEM ?

A

Beam electron

43
Q

What is the secondary electron in SEM ?

A

An electron from an atom in the sample knocked away by the primary electron

44
Q

What are backscattered electrons in SEM ?

A

A primary electron deflected back by the nucleus of an atom in the sample
-The bigger the nucleus, the more backscattered electrons

45
Q

How can you tell if a particle isn’t GSR ?

A
  • There are no known primers
    -no rounded shape
    -presence of other elements
46
Q

How does an SEM work ?

A
  • The beam electron knocks an electron out of an atom in the sample
    -An electron from a higher energy level in the sample atom drops to fill the gap
    -by conservation of energy an X-ray is emitted with the same energy as the drop the electron in the atom made

Analytical Techniques In Forensic Science (3 decks)

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