internal ballistics and gunshot residue Flashcards
(87 cards)
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’
2
Q
recovered firearms
sawn off shot gun
A
- Side by side or O/U twin barrel
- Easily concealable
- Large pellet spread
- Increasing popularity
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!
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
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
6
Q
3 types of ballistics
A
terminal
external
internal
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!
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
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?
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
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!
12
Q
2 alternative case materials
A
Low carbon steel ~ 0.1% carbons
aluminium
13
Q
give one advantage of low carbon steel case
A
very high tensile strength
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
15
Q
2 advantages of aluminium case materials
A
- Cheap – The main or perhaps only benefit really
- Relatively ductile but not all that strong
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
17
Q
the bullet-lead
A
- Relatively dense
- Will expand into barrel rifling without causing damage
- Deforms upon impact
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
19
Q
the bullet- solid
A
- Solid metal such as soft copper or in some case some very odd alloys
- Uncommon- specialist
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
21
Q
what is propulsion normally from
A
production of high pressure gas
22
Q
propellants- mechanical/ physical generation
A
Sprung- spring powered piston provides compression
Pre charged- either by pre charged HPA tank or CO2 bulb
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
24
Q
early compositions in propellants
A
based on black powder
25
black powder disadvantages
- Produces vast amounts of smoke
| - Causes fouling of barrels and weapon components degrading accuracy comparatively rapidly
26
black powder- uncommon in criminal activities
- 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
27
black powder substitutes
pyrodex
28
pyrodex
- Based on black powder
| - Contain additional oxidisers in addition to other components such as potassium perchlorate
29
pyrodex benefits
- 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
30
pyrodex- uncommon in criminal activities
- Not normally seen within a criminal GSR context
31
what are most modern propellants based upon and who discovered it
cellulose nitrate
Discovered by Christian Schönbein in 1846
32
simple nitration reaction for modern propellants
• 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
33
modern propellants- propellants are never sold in the raw gun cotton form
- 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
34
how are propellants typically sold
- 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
35
7 propellant additives
- 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
energetic materials
| single base propellants
- Consisting of a single energetic material
- Cellulose nitrate
- Dissolved in alcohol-ether
- Extruded into flakes, tubes, cylinders or similar
37
energetic materials
| multi base propellants
- 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
name 6 other components in propellants
```
stabilisers
plasticisers
flash supressants
moderators/ deterrents
colourants
graphite
```
39
why are stabilisers used in propellants
- 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
why are plasticisers used in propellants
- 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
why are flash suppressants used in propellants
- 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
why are moderators/deterrents used in propellants
- 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
why are colourants used in propellants
- 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
why is graphite used in propellants
- 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
what does grain size in propellant affect
rate of gas generation
46
small grain size of propellant
- 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
medium grain size of propellant
- 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
large grain size of propellant
- Slow burn – Large calibre rifles and canon
49
digressive burn
Rate of gas generation decreases with time
- Rapid rise in pressure and higher peak
- Cylindrical/flake
50
neutral burn
Rate of gas generation constant
| - Single perforation
51
progressive burn
– Rate of gas generation increases with time
| - Perforated or star shaped grain
52
typical propellant loads
- Entirely variable on cartridge and bullet combination
53
1 gramme is
15.43 grains (gr)
54
1 grain is
0.0648 grammes (g)
55
mass is measure in
grains (gr)
56
two main variants of brass cup
- Boxer primed – The most popular design
| - Berdan primed – Very much out of favour
57
how does brass cup contain primer composition
- Sometimes sealed with foil paper
| - Boxer type also includes anvil device
58
brass cup is
Friction and shock sensitive
59
how does brass cup allow initiation of main propellant charge
- Flash and hot material ignite propellant charge
| - Three main sizes available for small arms
60
primer sizes- small
Small –.175 inches in diameter (Rifle and Pistol)
| - Used in small calibres rifle and pistols – i.e. .223Rem or 9mm
61
primer sizes- large
Large –.210 inches in diameter (Rifle and Pistol)
| - Larger calibre Rifles and pistols – i.e .243Win, or .45ACP
62
shot gun- primer sizes
Shotgun –.209 inches in diameter (Standard and Magnum)
| - Generally longer than a typical primer to fit into the longer primer pocket of shotshells
63
all primers come in 2 forms
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
primer design
- 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
3 early primer compositions
mercury fulminate
chlorate
lead azide
66
mercury fulminate
- An innocuous looking grey-white powder
| - Friction and shock sensitive and also toxic – not a great combination!
67
practicals use of mercury fulminate
- Combustion products which contain Mercury have tendency to destroy the brass casing preventing re-use
68
mercury fulminate additives
- Commonly includes potassium chlorate (an oxidiser) to allow proper flame propagation
- Some fulminate primers contain ground glass to improve sensitivity
69
Chlorate compositions – K+ClO3-
- 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
Lead Azide – Relatively stable – Pb(N3)2
- 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
modern compositions-
Multi- component- SINOXID type
lead styphnate
- 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
modern compositions-
Multi- component- SINOXID type
Barium nitrate
Oxidising agent increasing burn rate and propagates flame/flash
73
Oxidising agent increasing burn rate and propagates flame/flash
antimony sulphide
May increase sensitivity
| Fuel to aid in flame propagation producing longer flash
74
Variants of SINOXID
| - Lead styphnate replaced with
May be augmented or even replaced with fully organic alternatives such as Tetrazene or diazodinitrophenol
75
Variants of SINOXID
| - barium nitrate replaced with
- 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
Variants of SINOXID
| - antimony sulphide replaced with
- 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
Multicomponent non toxic- SINTOX
- 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
an example of military primer composition
- 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
cartridge discharge
| primer initiation
- 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
propellant initiation
- 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
Particulate
| GSR, smoke, gas, lubricant and particulate
- 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
particulares- revolvers in particular are very leaky
- 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
particulate of semi automatics
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
Distribution form CZ85- study
- 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
p-GSR/o-GSR
| Two main categories of GSR
Inorganic GSR – p-GSR
Organic GSR – o-GSR
86
Inorganic GSR – p-GSR
- 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
Organic GSR – o-GSR
- 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
