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Materials identification > internal ballistics and gunshot residue > Flashcards

internal ballistics and gunshot residue Flashcards

1
Q

Recovered firearms

Baikal IZH-79 – Available converted £1200

A
  • Russian Makarov/PPK clone
  • Originally designed to fire tear gas or rubber pellets
  • 8mm blank
  • Readily converted to fire live ammunition 9mm K
  • Available as ‘assassination packages’
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2
Q

recovered firearms

sawn off shot gun

A
  • Side by side or O/U twin barrel
  • Easily concealable
  • Large pellet spread
  • Increasing popularity
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3
Q

recovered firearms

Ingram MAC-10/11

A
  • Sub-Machine gun
  • Chambered to fire 9mm P
  • Full auto – 1200+ RPM
  • 32 rounds emptied in under 2 seconds!
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4
Q

replica firearms

A
  • Beretta 92FS clone
  • Same size as the original
  • Similar weight
  • But this is a gas powered BB gun!
  • Purchase controlled by VCRA (2006)
  • Cannot be converted to fire live ammunition
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5
Q

police weaponry- varies upon force lines

A

Pistol – Inherently ‘safe’ designs favoured

  • Glock 17 – 9mm P – 17+1 capacity SLP
  • Sig Sauer P226 – 9mm P – 15+1 capacity SLP

SMG – Capable of semi-auto fire only

  • H&K MP5 SF – 9mm P – 30+1 capacity SLR
  • H&K MP7 – 4.6 x 30mm – used by MOD police

Rifle – Capable of semi-auto fire only
- H&K G36C SF – 5.56mm – 30+1 capacity SLR

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6
Q

3 types of ballistics

A

terminal
external
internal

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7
Q

terminal ballistics

A
  • Related to the interaction of the projectile with its target – In other words (in most cases) how a bullet interacts with living tissue!
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8
Q

external ballistics

A
  • Related to the passage of the expelled projectile through the air up until its interaction with the target – Considers drop, drift and other factors
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9
Q

internal ballistics

A
  • Related to all processes from the moment of initiation of a cartridge to the expulsion of the bullet from the barrel
  • Probably the most forensically important area of ballistics
  • What sort of information can it provide?
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10
Q

internal ballisitics

ammunition

A
  • Case
    • Normally brass, steel or aluminium
  • Bullet
    • A variety of designs to meet the needs of each application
  • Propellant
    • A variety of shapes, sizes and compositions
  • Primer
    • Several types
    • Various sizes
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11
Q

cartridge cases

A

Most frequently manufactured from cartridge Brass – An alloy of Copper (70%) and Zinc (30%)

  • Excellent tensile strength – Resistant to bursting from gas pressure
  • Ductile – Case will expand slightly when fired giving a good gas seal against the chamber of the weapon
  • Reusable – Can be reshaped and reloaded very easily with minimal equipment needed
  • Reshape-able – Allow the production of so called wildcat cartridges – e.g. .270win is really just a necked down .30-06
  • Corrosion resistant – Long term storage
  • soft enough not to damage working parts
  • Interestingly perfectly legal to buy over the internet without FAC!
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12
Q

2 alternative case materials

A

Low carbon steel ~ 0.1% carbons

aluminium

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13
Q

give one advantage of low carbon steel case

A

very high tensile strength

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14
Q

3 disadvantages to low carbon steel

A
  • Lower ductility than brass – Poorer gas seal
  • Prone to corrosion unless lacquered
  • Hard on working parts of a firearm
  • Generally limited to eastern European military manufacturers
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15
Q

2 advantages of aluminium case materials

A
  • Cheap – The main or perhaps only benefit really

- Relatively ductile but not all that strong

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16
Q

3 disadvantages of aluminium case materials

A
  • Generally limited to lower pressure rounds
  • Often coated (PTFE)
  • Cannot or rather should not be reused
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17
Q

the bullet-lead

A
  • Relatively dense
  • Will expand into barrel rifling without causing damage
  • Deforms upon impact
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18
Q

the bullet- jacketed

A
  • Normally a lead core with a gilding metal jacket
  • Less deformation and greater penetration
  • Some include an internal penetrator
  • Some may include hollow point or expanding tips
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19
Q

the bullet- solid

A
  • Solid metal such as soft copper or in some case some very odd alloys
  • Uncommon- specialist
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20
Q

name 8 shapes and designs of bullets

A 
lead round nose
wad cutter
semi wad cutter
full metal jacket
semi jacketed
semi jacketed hollow point
jacketed hollow point
special
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21
Q

what is propulsion normally from

A

production of high pressure gas

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22
Q

propellants- mechanical/ physical generation

A

Sprung- spring powered piston provides compression

Pre charged- either by pre charged HPA tank or CO2 bulb

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23
Q

propellants- chemical generation- conventional ammunition

A

A composition that will react rapidly to produce large quantities of hot gas
Solid or liquid compositions
Propulsion as a result of deflagration or low order explosion
Detonations extremely undesirable

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24
Q

early compositions in propellants

A

based on black powder

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25
Q

black powder disadvantages

A
  • Produces vast amounts of smoke

- Causes fouling of barrels and weapon components degrading accuracy comparatively rapidly

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26
Q

black powder- uncommon in criminal activities

A
  • Still popular with enthusiasts in muzzle loading firearms and BP revolvers which are only legal way of firing normal length pistols in the UK
  • Requires an explosives licence to buy and store
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27
Q

black powder substitutes

A

pyrodex

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28
Q

pyrodex

A
  • Based on black powder

- Contain additional oxidisers in addition to other components such as potassium perchlorate

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29
Q

pyrodex benefits

A
  • Less smoke – Clean burning gaseous exhaust
  • Less fouling – Less solid material formed
  • Less sensitive – Comparatively difficult to ignite
  • Not considered an explosive hence easily purchased and stored
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30
Q

pyrodex- uncommon in criminal activities

A
  • Not normally seen within a criminal GSR context
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31
Q

what are most modern propellants based upon and who discovered it

A

cellulose nitrate

Discovered by Christian Schönbein in 1846

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32
Q

simple nitration reaction for modern propellants

A

• Conc. H2SO4 + Conc. HNO3 in 2:1 ratio
• Addition of Cotton for 2-10 minutes
• Resultant product washed and neutralised
• Remaining acid contaminants may increase
sensitivity and decrease longevity
• Acid removal process vital to stability and many
manufacturers take days over this process

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33
Q

modern propellants- propellants are never sold in the raw gun cotton form

A
  • Most undergo a complex series of processes in order to obtain a more useable material which burns uniformly releasing gas as a controlled rate
  • formed by dissolving the NC in a solvent after the addition of various other materials designed to affect powder characteristics
  • These are then extruded through a die and are chopped into pellets or granules ready for sale
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34
Q

how are propellants typically sold

A
  • Propellants are typically sold for reloading as pellets, granules or powders of specific size and shape in 1lb (454g) tubs which retail for around £30-40 in UK
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35
Q

7 propellant additives

A
  • Additional energetic materials – To provide superior burn characteristics
  • Stabilisers – Increase shelf life and prevent decomposition
  • Plasticisers – Provide desirable mechanical properties
  • Flash suppressant materials – Minimise muzzle flash
  • Moderators/Deterrents – Alter burn rate
  • Colourants – Often purely marketing, the NC material itself is generally an unpleasant yellowish colour
  • Graphite – Lower sensitivity to static and allow the material to flow rather than caking in its packaging
36
Q

energetic materials

single base propellants

A
  • Consisting of a single energetic material
  • Cellulose nitrate
  • Dissolved in alcohol-ether
  • Extruded into flakes, tubes, cylinders or similar
37
Q

energetic materials

multi base propellants

A
  • Consisting of a two or three energetic materials
  • Nitrocellulose with…
  • Nitroglycerine or 2,4 DNT – Double base
  • Nitroguinidine – Triple base
  • Used to increase power and enhance other characteristics
38
Q

name 6 other components in propellants

A 
stabilisers
plasticisers
flash supressants 
moderators/ deterrents
colourants
graphite
39
Q

why are stabilisers used in propellants

A
  • Normally compounds used to neutralise the acidic decomposition products of the energetic components
  • Extend shelf-life and prevent sensitisation
  • Ethylcentralite (3-Diethyl-1,3-diphenylurea) or diphenylamine most common examples
40
Q

why are plasticisers used in propellants

A
  • Used to allow propellant to be extruded and cut more easily
  • May also lower ‘hygroscopicity’ (prevent it from absorbing moisture)
  • Ethylcentralite, triacetin, 2,4 DNT
41
Q

why are flash suppressants used in propellants

A
  • Minimise the flash that occurs as the weapon fires due to incomplete combustion
  • More common in military compositions for obvious reasons
  • Nitroguanidine, Ammonium or Potassium Salts
42
Q

why are moderators/deterrents used in propellants

A
  • Used to allow regulation of the initial rate of combustion
  • May also regulate burn characteristics of the propellant allowing slower release of gas
  • Particularly important in rifles where rapid gas production may cause over-pressure
  • Ethylcentralite, 2,4 DNT
43
Q

why are colourants used in propellants

A
  • May be used to impart a desirable colour for marketing purposes
  • May also be used for identification purposes
  • Variety of colours, although most are black or dark grey
44
Q

why is graphite used in propellants

A
  • To improve propellant flow and prevent caking or clumping
  • Makes life easier for the reloader
  • Prevent static build up which could potentially initiate premature initiation
45
Q

what does grain size in propellant affect

A

rate of gas generation

46
Q

small grain size of propellant

A
  • Fast burn – Pistols or short barrelled firearms
  • May cause overpressure in larger calibre rounds
  • Handloaders take care with powders to ensure that potentially lethal mix ups don’t occur
47
Q

medium grain size of propellant

A
  • Moderate burn – Rifles or large calibre pistols

- Gas is produced more slowly over a longer period of time to account for the longer rifle barrel

48
Q

large grain size of propellant

A
  • Slow burn – Large calibre rifles and canon
49
Q

digressive burn

A

Rate of gas generation decreases with time

  • Rapid rise in pressure and higher peak
  • Cylindrical/flake
50
Q

neutral burn

A

Rate of gas generation constant

- Single perforation

51
Q

progressive burn

A

– Rate of gas generation increases with time

- Perforated or star shaped grain

52
Q

typical propellant loads

A
  • Entirely variable on cartridge and bullet combination
53
Q

1 gramme is

A

15.43 grains (gr)

54
Q

1 grain is

A

0.0648 grammes (g)

55
Q

mass is measure in

A

grains (gr)

56
Q

two main variants of brass cup

A
  • Boxer primed – The most popular design

- Berdan primed – Very much out of favour

57
Q

how does brass cup contain primer composition

A
  • Sometimes sealed with foil paper

- Boxer type also includes anvil device

58
Q

brass cup is

A

Friction and shock sensitive

59
Q

how does brass cup allow initiation of main propellant charge

A
  • Flash and hot material ignite propellant charge

- Three main sizes available for small arms

60
Q

primer sizes- small

A

Small –.175 inches in diameter (Rifle and Pistol)

- Used in small calibres rifle and pistols – i.e. .223Rem or 9mm

61
Q

primer sizes- large

A

Large –.210 inches in diameter (Rifle and Pistol)

- Larger calibre Rifles and pistols – i.e .243Win, or .45ACP

62
Q

shot gun- primer sizes

A

Shotgun –.209 inches in diameter (Standard and Magnum)

- Generally longer than a typical primer to fit into the longer primer pocket of shotshells

63
Q

all primers come in 2 forms

A

Standard or rifle/magnum, with the latter pairing most appropriate for cartridges using propellant that is more difficult to ignite therefore requiring a more sustained ignition

64
Q

primer design

A
  • Will reliably ignite when struck with a firing pin/striker – Low failure rate
  • Will reliably ignite the entire propellant mixture – To maximise efficiency
  • Will not ignite when primer or cartridge is dropped – So not that sensitive!
  • Will not ignite when exposed to vibration during firing process – This is particularly relevant to high end big game rifles
  • Comparatively insensitive to extremes of environmental temperature
  • Efficiency must be retained at lower temperatures
  • Chemically stable – Will not decompose over time
  • Will not cause damage to firearm
  • Ideally non-toxic
65
Q

3 early primer compositions

A

mercury fulminate
chlorate
lead azide

66
Q

mercury fulminate

A
  • An innocuous looking grey-white powder

- Friction and shock sensitive and also toxic – not a great combination!

67
Q

practicals use of mercury fulminate

A
  • Combustion products which contain Mercury have tendency to destroy the brass casing preventing re-use
68
Q

mercury fulminate additives

A
  • Commonly includes potassium chlorate (an oxidiser) to allow proper flame propagation
  • Some fulminate primers contain ground glass to improve sensitivity
69
Q

Chlorate compositions – K+ClO3-

A
  • Armstrong’s mixture – often pacified with boron carbide
  • Often described as unpredictable and potentially very shock sensitive
  • Hygroscopic – Therefore limited shelf life
  • Decomposes to metallic oxides and chlorides which convert to corrosive compounds that may cause severe damage to barrels over time and are thus obsolete
70
Q

Lead Azide – Relatively stable – Pb(N3)2

A
  • In general less sensitive than fulminates
  • Reaction with copper leads to copper azide formation which is extremely sensitive to shock
  • Application in gas generators Airbags (Sodium Azide) but no longer common in primer compositions
71
Q

modern compositions-
Multi- component- SINOXID type

lead styphnate

A
  • Lead styphnate - Lead 2,4,6-trinitroresorcinate
    Shock sensitive primary initiator chemically related to both TNT and TNP
    Less sensitive than azides or fulminate although more sensitive to static – This is something which could potentially lead to issues in reloading!
72
Q

modern compositions-
Multi- component- SINOXID type

Barium nitrate

A

Oxidising agent increasing burn rate and propagates flame/flash

73
Q

Oxidising agent increasing burn rate and propagates flame/flash

antimony sulphide

A

May increase sensitivity

Fuel to aid in flame propagation producing longer flash

74
Q

Variants of SINOXID

- Lead styphnate replaced with

A

May be augmented or even replaced with fully organic alternatives such as Tetrazene or diazodinitrophenol

75
Q

Variants of SINOXID

- barium nitrate replaced with

A
  • Oxidiser may be replaced with…
    Strontium compounds – Strontium Nitrate (Also found in fireworks)
    Potassium (per)chlorates (Powerful oxidisers used in pyrotechnics)
    Stable peroxides – Zinc Peroxide
76
Q

Variants of SINOXID

- antimony sulphide replaced with

A
  • Antimony Sulphide fuel may be replaced with
    calcium Silicide – Flammable but moisture sensitive
    Aluminium – Prolongs flash and increases heat produced
    Rim fire variants may include ground glass frictionators
77
Q

Multicomponent non toxic- SINTOX

A
  • Diazodinitrophenol or Tetrazene derivatives
    Shock sensitive primary initiators
    Less sensitive than azides, fulminate or Lead Styphnate
    Less reliable and hence arguably less popular with firearms professionals
    Non Toxic – Less liable to cause elevated environmental lead levels
  • Zinc peroxide or similar
    Oxidising agent increases burn rate and aid flame propagation
  • Titanium or similar
    Fuel – Used to prolong the flash
78
Q

an example of military primer composition

A
  • US Military composition – M52A3B1
  • The recipe for a military priming composition
  • Lead Styphnate – 44% - Initiator
  • Barium Nitrate – 40% - Oxidiser
  • Calcium Silicide – 13% - Fuel
  • Acacia Gum – 1% - Binder and pacifier (CaSi2)
  • Acetylene Black – 1% - Colour
  • Styphnic Acid – 1% - Partly a preservative
79
Q

cartridge discharge

primer initiation

A
  • The firing pin or striker hits the centre of the primer
  • The anvil and primer composition are forced together
  • This ignites the primary initiator
  • Initiation of other components
  • White hot particulate forced through flash hole
  • Temperature ~1500⁰C
  • Pressure - ~1400psi
  • All with a few ms
80
Q

propellant initiation

A
  • As the primer derived hot gases enter the main cartridge body
  • The propellant will begin to burn rapidly
  • Producing vast quantities of gas
  • Temperature increases to ~3000⁰C+
  • Pressure in 105 kPa range (30,000+ PSI) although pressures of over 60,000 PSI are not uncommon in some calibres
  • Bullet is forced out down the barrel of the firearm and pressure begins to drop off
  • Bullet acceleration in the order of 10,000 G
  • 0-60mph in 0.00027s!
81
Q

Particulate

GSR, smoke, gas, lubricant and particulate

A
  • Rapidly expelled down the barrel and out any available gaps in the firearm
  • This is the likely mechanism of GSR deposition
  • In the same way that even the most careful smoker will always smell of cigarette smoke, the firer of a weapon will invariably be covered in GSR
82
Q

particulares- revolvers in particular are very leaky

A
  • Chambers/Barrel gap and rear of chamber
  • Note flash from cylinder gap
  • Covers shooters hands and surrounding areas in GSR material
  • Backwash will also cover clothing, face and hair
83
Q

particulate of semi automatics

A

SLP’s perhaps less intrinsically leaky in their design

  • There is no barrel/cylinder gap however, some of the deposition of material (other than backwash) may be the result of slide return and cartridge extraction
  • A secondary flash as barrel/chamber and slide separate may sometimes be seen and some GSR may also be deposited from the trigger area
  • Tendency to adhere to upper surfaces of hands, forearms, face and clothing
  • Possible directional bias
84
Q

Distribution form CZ85- study

A
  • Lubor Fojtáek et al
  • Note right hand distribution to particulate materials
  • Also distribution to rear again to the right side of the shooter
  • Note also the limits of detection in this case about 6m!
  • It is likely that distribution differs considerably between models and ammunition type
85
Q

p-GSR/o-GSR

Two main categories of GSR

A

Inorganic GSR – p-GSR

Organic GSR – o-GSR

86
Q

Inorganic GSR – p-GSR

A
  • GSR generally derived from the detonation of the primer but may include shaved materials from bullet and barrel
  • Normally metallic multi-element particulate – Pb-Ba-Sb for example
  • Few alternative sources
  • Forensically very significant
87
Q

Organic GSR – o-GSR

A
  • GSR generally derived from the propellant and its additives
  • Normally carbon containing particulate
  • Unburned propellant in particular
  • Nitrates and Nitrites
  • Alternative sources
  • May be less forensically significant

Materials identification (21 decks)

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