internal ballistics and gunshot residue Flashcards
Recovered firearms
Baikal IZH-79 – Available converted £1200
- 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’
recovered firearms
sawn off shot gun
- Side by side or O/U twin barrel
- Easily concealable
- Large pellet spread
- Increasing popularity
recovered firearms
Ingram MAC-10/11
- Sub-Machine gun
- Chambered to fire 9mm P
- Full auto – 1200+ RPM
- 32 rounds emptied in under 2 seconds!
replica firearms
- 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
police weaponry- varies upon force lines
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
3 types of ballistics
terminal
external
internal
terminal ballistics
- Related to the interaction of the projectile with its target – In other words (in most cases) how a bullet interacts with living tissue!
external ballistics
- Related to the passage of the expelled projectile through the air up until its interaction with the target – Considers drop, drift and other factors
internal ballistics
- 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?
internal ballisitics
ammunition
- 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
cartridge cases
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!
2 alternative case materials
Low carbon steel ~ 0.1% carbons
aluminium
give one advantage of low carbon steel case
very high tensile strength
3 disadvantages to low carbon steel
- 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
2 advantages of aluminium case materials
- Cheap – The main or perhaps only benefit really
- Relatively ductile but not all that strong
3 disadvantages of aluminium case materials
- Generally limited to lower pressure rounds
- Often coated (PTFE)
- Cannot or rather should not be reused
the bullet-lead
- Relatively dense
- Will expand into barrel rifling without causing damage
- Deforms upon impact
the bullet- jacketed
- 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
the bullet- solid
- Solid metal such as soft copper or in some case some very odd alloys
- Uncommon- specialist
name 8 shapes and designs of bullets
lead round nose wad cutter semi wad cutter full metal jacket semi jacketed semi jacketed hollow point jacketed hollow point special
what is propulsion normally from
production of high pressure gas
propellants- mechanical/ physical generation
Sprung- spring powered piston provides compression
Pre charged- either by pre charged HPA tank or CO2 bulb
propellants- chemical generation- conventional ammunition
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
early compositions in propellants
based on black powder
black powder disadvantages
- Produces vast amounts of smoke
- Causes fouling of barrels and weapon components degrading accuracy comparatively rapidly
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
black powder substitutes
pyrodex
pyrodex
- Based on black powder
- Contain additional oxidisers in addition to other components such as potassium perchlorate
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
pyrodex- uncommon in criminal activities
- Not normally seen within a criminal GSR context
what are most modern propellants based upon and who discovered it
cellulose nitrate
Discovered by Christian Schönbein in 1846
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
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
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
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
energetic materials
single base propellants
- Consisting of a single energetic material
- Cellulose nitrate
- Dissolved in alcohol-ether
- Extruded into flakes, tubes, cylinders or similar
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
name 6 other components in propellants
stabilisers plasticisers flash supressants moderators/ deterrents colourants graphite
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
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
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
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
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
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
what does grain size in propellant affect
rate of gas generation
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
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
large grain size of propellant
- Slow burn – Large calibre rifles and canon
digressive burn
Rate of gas generation decreases with time
- Rapid rise in pressure and higher peak
- Cylindrical/flake
neutral burn
Rate of gas generation constant
- Single perforation
progressive burn
– Rate of gas generation increases with time
- Perforated or star shaped grain
typical propellant loads
- Entirely variable on cartridge and bullet combination
1 gramme is
15.43 grains (gr)
1 grain is
0.0648 grammes (g)
mass is measure in
grains (gr)
two main variants of brass cup
- Boxer primed – The most popular design
- Berdan primed – Very much out of favour
how does brass cup contain primer composition
- Sometimes sealed with foil paper
- Boxer type also includes anvil device
brass cup is
Friction and shock sensitive
how does brass cup allow initiation of main propellant charge
- Flash and hot material ignite propellant charge
- Three main sizes available for small arms
primer sizes- small
Small –.175 inches in diameter (Rifle and Pistol)
- Used in small calibres rifle and pistols – i.e. .223Rem or 9mm
primer sizes- large
Large –.210 inches in diameter (Rifle and Pistol)
- Larger calibre Rifles and pistols – i.e .243Win, or .45ACP
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
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
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
3 early primer compositions
mercury fulminate
chlorate
lead azide
mercury fulminate
- An innocuous looking grey-white powder
- Friction and shock sensitive and also toxic – not a great combination!
practicals use of mercury fulminate
- Combustion products which contain Mercury have tendency to destroy the brass casing preventing re-use
mercury fulminate additives
- Commonly includes potassium chlorate (an oxidiser) to allow proper flame propagation
- Some fulminate primers contain ground glass to improve sensitivity
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
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
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!
modern compositions-
Multi- component- SINOXID type
Barium nitrate
Oxidising agent increasing burn rate and propagates flame/flash
Oxidising agent increasing burn rate and propagates flame/flash
antimony sulphide
May increase sensitivity
Fuel to aid in flame propagation producing longer flash
Variants of SINOXID
- Lead styphnate replaced with
May be augmented or even replaced with fully organic alternatives such as Tetrazene or diazodinitrophenol
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
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
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
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
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
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!
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
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
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
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
p-GSR/o-GSR
Two main categories of GSR
Inorganic GSR – p-GSR
Organic GSR – o-GSR
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
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
