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Analytical Techniques In Forensic Science > Forensic Ballistics > Flashcards

Forensic Ballistics Flashcards

(92 cards)

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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

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20
Q

How is primer GSR analyzed?

A

SEM- highly magnified images and chemical analysis

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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

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22
Q

What are advantages of primer GSR?

A

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

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23
Q

What is the composition of primers?

A

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

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24
Q

What is an oxidizer?

A

Produces oxygen to enable combustion

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25
What is a sensitizer?
Added to ammunition primers to make them more sensitive
26
What is a frictonator?
Substance that increases the sensitivity of the primer mixture to reduce the chance of misfire
27
What is the primer composition of sinoxyd ?
Lead Styphnate -explosive Barium Nitrate- oxidizer Lead Dioxide- oxidizer Tetracene- sensitizer Antimony Sulphide-fuel/frictionator Calcium Silicide- fuel/frictionator
28
How long does GSR stay on bags, windows and vehicles ?
Depends on circumstances and cleaning
29
How long does GSR stay on clothing ?
Discarded clothing and pockets can be indefinite but clothing that is worn continuously up to 24 hours
30
How long does GSR stay on hands, face and hair ?
Hands- up to 4 hours Face - up to 6 hours Hair- up to 12 hours
31
What are types 1-3 of GSR ?
Type 1 - Lead, barium and antimony. Type 2 - Lead, barium, antimony and aluminium. Type 3 - Lead, barium, antimony and tin.
32
How is the calibre of a 20-gauge shotgun defined ?
The diameter of a solid sphere of lead weighing 1/20th of a pound
33
What are the different methods of detecting GSR ?
Bulk methods - colour tests SEM
34
Why are bulk methods unreliable ?
The elements are common in the environment and doesn’t tell you whether the elements are in one particle
35
Why is SEM a better method of detection ?
-Analyses individual particles -Distinguishes between different primers -tells if the elements are in one particle
36
Why is GSR often round ?
Formed under high pressure
37
How are samples of GSR taken ?
-adhesive tapes mounted on aluminum stubs and carbon coated -Now pre-prepared circular stubs more common
38
What level of GSR is considered very high ?
>50 particles
39
Why are armed police officers likely to have GSR on their hands and clothing ?
As they carry firearms so they more likely to have high levels of GSR on them if they’ve recently fired their gun.
40
Why can armed police officers potentially ruin the evidence of a case ?
If the residue is the same as crime ammunition it can be impossible to determine the source
41
How must specimens in a SEM be ?
In a vacuum
42
What is the primary electron in SEM ?
Beam electron
43
What is the secondary electron in SEM ?
An electron from an atom in the sample knocked away by the primary electron
44
What are backscattered electrons in SEM ?
A primary electron deflected back by the nucleus of an atom in the sample -The bigger the nucleus, the more backscattered electrons
45
How can you tell if a particle isn’t GSR ?
- There are no known primers -no rounded shape -presence of other elements
46
How does an SEM work ?
- 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
47
What is a comparison microscope ?
Two microscopes that are joined together using an optical bridge allowing two objects to be seen under a microscope simultaneously and compared side by side
48
What does the use of a comparison microscope avoid ?
The observer having to rely on memory when comparing two objects
49
Who developed comparison microscopes ?
Philip O. Gravelle
50
What do modern comparison microscopes have ?
LED illumination, digital imaging and video capabilities
51
What is parfocality and parcentricity ?
When objectives are perfocal and parcentric, the image remains centred and focused even as magnification changes
52
What is aperture and iris diaphragms ?
Ability to vary the depth of field as needed, to observe the base of an impression while keeping the alignment of tool marks that were observed on the sides of the impression
53
What are the different evidence types ?
-fibres -tool marks -bullets -cartridge cases -paint
54
How do tools leave a mark ?
The tool is harder than the surface it comes into contact with and leaves a mark in the softer surface
55
What do mass produced tools have to do?
Unique microscopic features that will create distinguishable marks
56
What are static marks ?
The tool is pressed into a softer material
57
What is a dynamic mark ?
The tool slides or scratches across a surface
58
What is a cutting mark ?
Pressure applied at one or both sides of an object
59
What is a multi-stroke mark ?
Repetitive action like sawing
60
What are class features ?
Common to all items of a particular type (type of tool, dimensions)
61
What are sub-class features ?
Not unique to an individual tool, but allows some discrimination between groups of tools of the same class
62
What are individual characteristics ?
Features arising at random during the manufacturing process or through normal use (striations, defects)
63
What are indentation marks ?
Made when a tool is pressed against a softer surface- may indicate information such as the size of the tool
64
What are abrasion marks ?
Made when a tool is placed against another object and moved parallel to and across the object with pressure applied
65
What cut marks do knives leave ?
-V shaped cut in surface -Microscopic striations
66
What cut marks do saws leave ?
-Square bottomed cut in surface -striations visible to naked eye
67
What cut marks do axes leave ?
-V shaped cut in surface -Much wider than knife cut -Maybe impact fractures around cut
68
How is tool mark evidence examined if possible ?
Collected from the scene and taken to the lab
69
If tool mark evidence can’t be taken to the lab how is it examined ?
Castings preserve impressions of the tool mark
70
What materials are used to make castings of tool marks ?
A variety of silicone or rubber-based casting materials can be used to record impression marks (MikroSil)
71
What should not be done with the tool mark evidence ?
Do not attempt to fit the suspects tool into the tool mark as any contact may alter the mark
72
What are test marks used for?
A variety of test marks are made at different angles and pressures to compare with the crime scene mark
73
What marks are left from bullets ?
- rifling marks -Slippage (skid marks)
74
What marks are left from cartridge cases ?
Impressions- - firing pin -breech mark -ejector mark Striated action marks- -Chamber marks -shear marks -firing pin drag marks -extractor marks -ejector marks
75
What is rifling ?
A pattern of channels that run the length of a firearm barrel, manufactured with a helical pattern or twist
76
What is the purpose of rifling ?
Impart a spin on the bullet along its long axis, which stabilises the projectile and allows it to travel more accurately.
77
Bore diameter
This is the distance measured between two opposite land and is considered as the calibre of the firearm
78
Width of lands
Land width is dependent on the bore diameter, groove width and number. The lands are a remainder of the circumference after all the groove width
79
Width of grooves
This is measured as the shortest distance between the two sides or edges of a groove
80
Pitch of rifling
It is a measure of the twisting of the land and grooves. It refers to the distance advance by rifling in one complete run (360 degrees)
81
What does damage to the bullet do ?
-Make examination difficult and affect markings -Rifling impressions can be seriously degraded and appear very blurry
82
What is blowby ?
- escaping of gases past a fired bullet while the bullet is still in the barrel -the high- pressure gases are at a very high temp and can melt or etch the surface of lead bullets
83
What are breech face impressions ?
-fired cartridge cases are identified as having been fired by a specific firearm -the recoil of the firearm forces the cartridge case against the breech face with very high pressure -marks on the breech face are imprinted on the cartridge especially the primer
84
What are firing pin marks ?
If the nose of the firing pin has manufacturing imperfections or damage, these potentially unique characteristics can be impressed into the metal of the primer
85
what are ejector marks ?
- can be striated or impressed -impressed can indicate that the round was fired in the suspect firearm rather than just cycled through the firearm and ejected while still live
86
What are chamber marks ?
cartridge cases expand when fired pressing out against the walls of the chamber. When they are pulled out of the chamber, the sides of the cartridge case can be scratched
87
What are the different types of chamber marks ?
-banded striae -banded spiral -fluting -ramp bulging -diagonal -rust
88
What are shear marks ?
-recoil forces the cartridge case backwards and the primer is pushed into the firing pin hole -the cartridge case moves down slightly as the action opens -the part of the primer in the firing pin hole is sheared downwards
89
What are firing pin drag marks ?
-As the cartridge case recoils it drops slightly -this causes the firing pin to drag across the primer
90
What are extractor marks ?
- the extractor is a claw shaped part that pulls out the cartridge case -the claw hooks into the extractor groove on the cartridge -as the slide moves back with recoil, the extractor pulls the cartridge back to be ejected
91
What happens if a suspect firearm is recovered ?
Test fire rounds and compare bullets and cartridge cases with those from the crime scene
92
What happens if the firearm isn’t recovered ?
Compare crime scene bullets and cartridge cases with the database: NABIS

Analytical Techniques In Forensic Science (6 decks)

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