Internal ballistics and gunshot residue

Question 1

what is terminal ballistics

Answer 1

related to the interaction of the projectile with its target

Question 2

external ballistics

Answer 2

Related to the passage of the expelled projectile through the air up until its interaction with the target

Considers drop, drift etc

Question 3

internal ballistics

Answer 3

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

Question 4

4 parts of ammunition

Answer 4

case
bullet
propellant
primer

Question 5

what is the case of ammunition usually made from?

Answer 5

brass
steel
aluminium

Question 6

what is cartridge brass

Answer 6

70% copper

30% zinc

Question 7

advantages of cartridge brass in cartridge cases

Answer 7

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

Question 8

give two alternative case materials

Answer 8

low carbon steel

aluminium

Question 9

advantage of low carbon steel as a cartridge case

Answer 9

Very high tensile strength

Question 10

disadvantages of low carbon steel as a cartridge case

Answer 10

Lower ductility than brass – Poorer gas seal

Prone to corrosion unless lacquered

Hard on working parts of a firearm

Question 11

advantage of aluminium as a cartridge case

Answer 11

cheap

Question 12

disadvantages of aluminium as a cartridge case

Answer 12

Relatively ductile but not all that strong

Generally limited to lower pressure rounds

Often coated (PTFE)

should not be reused

Question 13

the bullet - lead

Answer 13

Relatively dense

Will expand into barrel rifling without causing damage

Deforms upon impact

Question 14

the bullet - jacketed

Answer 14

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

Question 15

the bullet - solid

Answer 15

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

Uncommon – Specialist

Question 16

give 8 examples of shapes and designs of bullets

Answer 16

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

Question 17

mechanical/physical generation - air rifles

Answer 17

propulsion is provided by mechanically or physically

Sprung – Spring powered piston provides compression

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

Question 18

chemical generation - conventional ammunition

Answer 18

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

Question 19

what is black powder made up of

Answer 19

Potassium Nitrate – 75 parts

Charcoal – 15 Parts

Sulphur – 10 Parts

Question 20

name 2 disadvantages of black powder

Answer 20

Produces vast amounts of smoke

Causes fouling of barrels and weapon components degrading accuracy comparatively rapidly

Question 21

what is pyrodex a substitute of?

Answer 21

black powder

Question 22

what does pyrodex contain?

Answer 22

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

Question 23

4 benefits of pyrodex

Answer 23

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

Question 24

what are modern propellants based upon

Answer 24

cellulose nitrate

discovered by Christian Schönbein in 1846

Question 25

what is the nitration reaction for modern propellants

Answer 25

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

Question 26

propellants are never sold in the raw guncotton form

Answer 26

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

Question 27

how are pellets typically sold

Answer 27

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

Question 28

name 7 propellant additives

Answer 28

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

Question 29

single-base propellants

Answer 29

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

Question 30

multi-base propellants

Answer 30

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

Question 31

name 6 other components found in propellants

Answer 31

``` stabilisers plasticisers flash suppressants moderators/deterrents colourants graphite ```

Question 32

why are stabilisers put in propellants

Answer 32

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

Question 33

why are plasticisers put in propellants

Answer 33

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

Question 34

why are flash suppressants put in propellants

Answer 34

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

Question 35

why are moderators/deterrents put into propellants

Answer 35

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

Question 36

why are colourants put into propellants

Answer 36

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

Question 37

why is graphite put into propellants

Answer 37

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

Question 38

how does grain size affect propellants

Answer 38

affects rate of gas generation

Question 39

small grain propellants

Answer 39

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

Question 40

medium grain propellants

Answer 40

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

Question 41

large grain propellants

Answer 41

slow burn - large calibre rifles and canon

Question 42

digressive burn

Answer 42

Rate of gas generation decreased with time Rapid rise in pressure and higher peak Cylindrical/flake

Question 43

neutral burn

Answer 43

rate of gas generation constant single perforation

Question 44

progressive burn

Answer 44

Rate of gas generation increases with time Perforated or star shaped grain

Question 45

what is 1gram in grains

Answer 45

15.43gr

Question 46

what is 1 grain in grams

Answer 46

0.0648g

Question 47

what are the 2 variants of brass cup

Answer 47

Boxer primed – The most popular design Berdan primed – Very much out of favour

Question 48

primer construction

Answer 48

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

Question 49

primer sizes

Answer 49

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

Question 50

what two forms to primers come in

Answer 50

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

Question 51

primer design

Answer 51

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

Question 52

name 3 early primer compositions

Answer 52

mercury fulminate chlorate compositions lead azide

Question 53

mercury fulminate

Answer 53

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

Question 54

chlorate compositions

Answer 54

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

Question 55

lead azide

Answer 55

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

Question 56

name 3 modern primer compositions

Answer 56

lead styphnate barium nitrate antimony sulphide

Question 57

lead styphnate

Answer 57

Shock sensitive primary initiator chemically related to both TNT and TNP Less sensitive than azides or fulminate although more sensitive to static

Question 58

barium nitrate

Answer 58

Oxidising agent increasing burn rate and propagates flame/flash

Question 59

antimony sulphide

Answer 59

May increase sensitivity Fuel to aid in flame propagation producing longer flash

Question 60

diazodnitrophenol or tetrazene derivatives - multi component non toxic SINTOX

Answer 60

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

Question 61

zinc peroxide - multi component non toxic SINTOX

Answer 61

Oxidising agent increases burn rate and aid flame propagation

Question 62

titanium - multi component non toxic SINTOX

Answer 62

Fuel – Used to prolong the flash

Question 63

name a SINOXID variant

Answer 63

lead styphante

Question 64

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

Answer 64

Strontium compounds – Strontium Nitrate (Also found in fireworks) Potassium (per)chlorates (Powerful oxidisers used in pyrotechnics) Stable peroxides – Zinc Peroxide

Question 65

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

Answer 65

Calcium Silicide – Flammable but moisture sensitive Aluminium – Prolongs flash and increases heat produced Rim fire variants may include ground glass frictionators

Question 66

primer initiation - cartridge discharge

Answer 66

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

Question 67

what is the temperature and pressure during primer initiation

Answer 67

temp - 1500 degrees | pressure - 1400psi

Question 68

propellant initiation - cartridge discharge

Answer 68

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

Question 69

GSR, smoke, gas, lubricant and particulate

Answer 69

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

Question 70

revolvers are 'leaky'

Answer 70

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

Question 71

semi-automatics - particulate

Answer 71

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

Question 72

what are the two main categories of GSR

Answer 72

inorganic organic

Question 73

inorganic GSR

Answer 73

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

Question 74

organic GSR

Answer 74

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