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Materials Identification > Internal ballistics and gunshot residue > Flashcards

Internal ballistics and gunshot residue Flashcards

1
Q

what is terminal ballistics

A

related to the interaction of the projectile with its target

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2
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 etc

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3
Q

internal ballistics

A

Related to all processes from the moment of initiation of a cartridge to the repulsion of the bullet from the barrel

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4
Q

4 parts of ammunition

A

case
bullet
propellant
primer

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5
Q

what is the case of ammunition usually made from?

A

brass
steel
aluminium

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6
Q

what is cartridge brass

A

70% copper

30% zinc

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7
Q

advantages of cartridge brass in cartridge cases

A

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

Corrosion resistant – Long term storage

Soft enough not to damage working parts

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8
Q

give two alternative case materials

A

low carbon steel

aluminium

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9
Q

advantage of low carbon steel as a cartridge case

A

Very high tensile strength

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10
Q

disadvantages of low carbon steel as a cartridge case

A

Lower ductility than brass – Poorer gas seal

Prone to corrosion unless lacquered

Hard on working parts of a firearm

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11
Q

advantage of aluminium as a cartridge case

A

cheap

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12
Q

disadvantages of aluminium as a cartridge case

A

Relatively ductile but not all that strong

Generally limited to lower pressure rounds

Often coated (PTFE)

should not be reused

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13
Q

the bullet - lead

A

Relatively dense

Will expand into barrel rifling without causing damage

Deforms upon impact

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14
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 also include a hollow point or ‘expanding’ tips

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15
Q

the bullet - solid

A

Solid metal such as soft copper or in some cases some very odd alloys

Uncommon – Specialist

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16
Q

give 8 examples of shapes and designs of bullets

A 
lead round nose
was cutter
semi jacketed
semi jacketed hollow point
special
jacketed hollow point
full metal jacket
semi wad cutter
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17
Q

mechanical/physical generation - air rifles

A

propulsion is provided by mechanically or physically

Sprung – Spring powered piston provides compression

Pre-charged – Either pre-charged HPA tank or CO2 bulb

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18
Q

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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19
Q

what is black powder made up of

A

Potassium Nitrate – 75 parts

Charcoal – 15 Parts

Sulphur – 10 Parts

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20
Q

name 2 disadvantages of black powder

A

Produces vast amounts of smoke

Causes fouling of barrels and weapon components degrading accuracy comparatively rapidly

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21
Q

what is pyrodex a substitute of?

A

black powder

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22
Q

what does pyrodex contain?

A

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

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23
Q

4 benefits of pyrodex

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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24
Q

what are modern propellants based upon

A

cellulose nitrate

discovered by Christian Schönbein in 1846

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25
Q

what is the 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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26
Q

propellants are never sold in the raw guncotton 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

These materials are generally 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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27
Q

how are pellets 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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28
Q

name 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

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29
Q

single-base propellants

A

Consisting of a single energetic material

Cellulose nitrate

Dissolved in alcohol-ether

Extruded into flakes, tubes, cylinders or similar

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30
Q

multi-base propellants

A

Consisting of 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

31
Q

name 6 other components found in propellants

A 
stabilisers
plasticisers
flash suppressants
moderators/deterrents
colourants
graphite
32
Q

why are stabilisers put 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

33
Q

why are plasticisers put in propellants

A

Used to allow propellant to be extruded and cut more easily

May also lower ‘hygroscopicity’ (prevent from absorbing moisture)

Ethylcentralite, triacetin, 2,4 DNT

34
Q

why are flash suppressants put 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

35
Q

why are moderators/deterrents put into 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

36
Q

why are colourants put into 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

37
Q

why is graphite put into 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

38
Q

how does grain size affect propellants

A

affects rate of gas generation

39
Q

small grain propellants

A

Fast burn – Pistols or short barrelled firearms

May cause overpressure in larger calibre rounds

Hand loaders take care with powders to ensure that potentially lethal mix ups don’t occur

40
Q

medium grain propellants

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

41
Q

large grain propellants

A

slow burn - large calibre rifles and canon

42
Q

digressive burn

A

Rate of gas generation decreased with time

Rapid rise in pressure and higher peak

Cylindrical/flake

43
Q

neutral burn

A

rate of gas generation constant

single perforation

44
Q

progressive burn

A

Rate of gas generation increases with time

Perforated or star shaped grain

45
Q

what is 1gram in grains

A

15.43gr

46
Q

what is 1 grain in grams

A

0.0648g

47
Q

what are the 2 variants of brass cup

A

Boxer primed – The most popular design

Berdan primed – Very much out of favour

48
Q

primer construction

A

Contains priming composition

  • Sometimes sealed with foil paper
  • Boxer type also includes anvil device

Friction and shock sensitive

Allows initiation of main propellant charge

  • Flash and hot material ignite propellant charge
  • Three main sizes available for small arms
49
Q

primer sizes

A

3 main primer sizes for boxed primed cartridges

  • Small –.175 inches in diameter (Rifle and Pistol)
    Used in small calibres rifle and pistols – i.e. .223Rem or 9mm
  • Large –.210 inches in diameter (Rifle and Pistol)
    Larger calibre Rifles and pistols – i.e .243Win, or .45ACP
  • Shotgun –.209 inches in diameter (Standard and Magnum)

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

50
Q

what two forms to primers come in

A

standard
rifle/magnum

latter pairing most appropriate for cartridges using propellant that is more difficult to ignite therefore requiring a more sustained ignition

51
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

52
Q

name 3 early primer compositions

A

mercury fulminate
chlorate compositions
lead azide

53
Q

mercury fulminate

A

An innocuous looking grey-white powder

Friction and shock sensitive and also toxic

Combustion products which contain Mercury have tendency to destroy the brass casing (as a result of amalgamation) preventing re-use

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

54
Q

chlorate compositions

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

55
Q

lead azide

A

Relatively stable

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

56
Q

name 3 modern primer compositions

A

lead styphnate

barium nitrate

antimony sulphide

57
Q

lead styphnate

A

Shock sensitive primary initiator chemically related to both

TNT and TNP

Less sensitive than azides or fulminate although more sensitive to static

58
Q

barium nitrate

A

Oxidising agent increasing burn rate and propagates flame/flash

59
Q

antimony sulphide

A

May increase sensitivity

Fuel to aid in flame propagation producing longer flash

60
Q

diazodnitrophenol or tetrazene derivatives - multi component non toxic SINTOX

A

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

61
Q

zinc peroxide - multi component non toxic SINTOX

A

Oxidising agent increases burn rate and aid flame propagation

62
Q

titanium - multi component non toxic SINTOX

A

Fuel – Used to prolong the flash

63
Q

name a SINOXID variant

A

lead styphante

64
Q

in SINOXID, the oxidiser may be replaced with what 3 possible things

A

Strontium compounds – Strontium Nitrate (Also found in fireworks)

Potassium (per)chlorates (Powerful oxidisers used in pyrotechnics)

Stable peroxides – Zinc Peroxide

65
Q

in SINOXID, the antimony sulphide fuel can be possibly replaced with what 3 things

A

Calcium Silicide – Flammable but moisture sensitive

Aluminium – Prolongs flash and increases heat produced

Rim fire variants may include ground glass frictionators

66
Q

primer initiation - cartridge discharge

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

all within few ms

67
Q

what is the temperature and pressure during primer initiation

A

temp - 1500 degrees

pressure - 1400psi

68
Q

propellant initiation - cartridge discharge

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

69
Q

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

70
Q

revolvers are ‘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

71
Q

semi-automatics - particulate

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

72
Q

what are the two main categories of GSR

A

inorganic

organic

73
Q

inorganic 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

74
Q

organic 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 (17 decks)

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