Gun shot residue (GSR) comprises gases and particles that are ejected from a firearm when it is discharged. GSR can be found on the hands of the shooter, clothing of victims, and other surfaces near the firearm. It is composed of inorganic particles like lead, antimony, and barium as well as organic compounds from the propellant. GSR is collected using wet or dry methods and analyzed using chemical tests that detect specific elements or compounds, or instrumental methods like scanning electron microscopy, neutron activation analysis, and x-ray fluorescence which can identify elemental components. Analyzing GSR is forensically relevant for determining the firing range, reconstructing crime scenes, identifying the firearm and cartridge used, and linking suspects

1. University of Lucknow
Department of Anthropology
Forensic Science
Gun Shot Residue Prepared By
Mohd Hamza

2. Gun Shot Residue
What is GSR?
Production and dependence upon
Range.
Where is it found?
Its Composition and Classification.
How is it collected?
Methods for its detection and analysis.
Forensic Relevance.

3. What is Gun Shot Residue?
• Gun Shot Residue (GSR) also known as CDR (cartridge discharge
residue) and FDR (firearm discharge residue) comprises gases, non-
volatile, visible and invisible particles which may be unburnt or
partially burnt coming from Barrel, Primer, Propellant, Cartridge,
Bullet and Firearm.
• There detection location analysis plays an important role in
investigative procedures involving usage of any type of firearm.

4. Where is it found?
• GSR may be looked for
• On the hands - mainly present on thumb, trigger finger and web of
hand
• On the clothes of the victim, if the human being is the target
• Intermediate targets may also have GSR depositions
• Inside of cartridge cases and barrel may have GSR. In addition outside
surface of barrel can also be examined for GSR.
• Fired projectiles may also be examined for gunshot residue.

6. Production and dependence upon Range.
Distant Range
• In the case of distant-range firing there will be no GSR like blackening, scorching and
tattooing as well as metallic chips around the hole of entrance. All of them will not
appear and remain absent.
• However, during the passage of a bullet through the rifled barrel and through a defective,
roughened or country made weapons (also termed improvised weapons), small
fragments of metal are cut and propelled in the direction in which projectiles are ejected.
• In view of the fact that these particles are heavier than the powder grains they travel
longer distance beyond the maximum distance to which powder grains are ejected.

7. Close Range
• In close range firing, dust ring, burning,
blackening and tattooing appears as GSR
on the target as shown in the figure below.
The burning of skin is accompanied in by
the track shown in the figure due to its
reaction with carbon monoxide which is also
a product of combustion (GSR).
• In case of contact firing, it is the entry which has projectiles and
other GSR in the track of the hole in additions to the above
mentioned locations GSR can be located at the following places or articles:
• Articles around the target or around the shooter or both, depending upon the
nature of firing, may contain GSR.

8. • Clothes and other garments of the victim, which act like intermediate
targets, may have GSR on them.
• The GSR particles are dispersed in the air. Being light particles, they
continue in the air for a long time. They may be transferred to a
surface, which comes in contact with air, or surface, which already
has GSR.
• Intermediate targets, other than clothes, may also have GSR when a
projectile hits a glass windowpane or a wooden door. The holes
created by a bullet in a glass pane or wooden door would carry
especially the GSR, load particles, and many others depending on the
cartridge cases and primer.

9. Contact Range
• While a weapon is fired, and the muzzle end is expected to touch the target
it is termed contact range.
• When the contact is tight and pressing the surface of a target uniformly
and close, the skin surrounding the perforation is not tattooed or
blackened with embedded powder grains as in a case of close-range shot
indicating absence of GSR, but this may not happen, always.
• Occasionally, some burned and unburned powder grains may get deposited
on the skin in and around the margins of entrance wound.
• It is just possible that the weapon may be lifted, on one side due to
manufacturing defect in country made weapon or due to careless handling
by the shooter or efforts made by victim. To escape an attack, resulting in
losing of light contact giving rise to escape or burned and unburned
powder grain and their deposition on the skin.
• In a tight and proper contact, all the GSR as well as ammunition would be
driven into track made by the ammunition through the entrance hole.

10. •Hands of shooter- When a firearm is fired it not only
shoots GSR and projectile forward but some of the
particles are backfired and thereby spread on the
hands of the person shooting it.
•Clothes- Clothes of the victim lie as the first line
between victim’s body and projectile and the
incoming GSR also the particles stuck on the projectile
get wiped of as it enters through the clothes due to
motion and friction of the projectile.

11. •Intermediate Target- GSR may also be looked upon
the intermediate materials bullet passes through
before reaching the final target in many of the cases
glass panes are a commonly found intermediate
targets.
•Barrel- If not manipulated can be a source of GSR as
well it may be found inside or outside the barrel.

12. Composition and Classification.
GSR
Inorganic Organic
• Bullet- Lead. Nitrocellulose
• Barrel- Iron Nitro-glycerine
• Primer- Antimony, Barium, Lead Lubricants (Paraffin)
• Propellant- Nitrate, Nitrite, CO, C.
• Cartridge- Nickel, Zinc, Copper

13. How it collected?
Wet Methods
• A cellophane sheet is impregnated with acetic acid, after
impregnation the same is pressed against the site. It will pick up bad
particles.
• A solution of cellulose acetate is applied bearing the GSR. When it
gets dried up it may be peeled off and the gunshot residues will be
picked up by the cast.
• The site bearing the powder marks is sprayed with a colloidal
solution. The film is reinforced with nylon fibres. The reformed film
that picks up the GSR is peeled off on drying.
• The residues in the barrel are collected by washing the same with hot
distilled water. The washings are tested for constituents of the gun
powder residues

14. Dry Methods
• Use of adhesive tapes. An inert adhesive tape (or an adhesive
aluminium tape) is pressed against the site bearing the GSR many a
times to pick up the desired GSR which can then be subsequently
selected for examination.
• Technique of Swabbing- A clean piece of cloth or a filter paper is
moistened with an organic solvent, which may by acetone, alcohol or
ether and the site suspected of containing GSR is swabbed. The swabs
are collected and extracted.
• Vacuum Lifting Technique- This technique is especially suitable for
collecting of GSR from clothes. The material deposited on the filter
dust is extracted with a suitable solvent for further processing.

15. Infrared Detection
• Sometimes the lack of colour contrast between the powder and the
garment or presence of heavily encrusted deposits of blood can
obscure the visual detection of gun powder. Often an infrared
photograph of suspect area, on the garment, overcomes such the
problem.
Fabric bearing GSR marks
invisible to naked eyes due to
colour contrast
Same Fabric under IR
Photography

16. Methods of Collection and Analysis.
Chemical Tests Instrumental Tests
• Sodium Rhodizonate Scanning Electron Microscope
• Walker Test Transmission Electron Microscope
Neutron Activation Analysis
• Marshall Test X-Ray Florescence
• Tewari Test
• Lunge’s Reagent

17. Chemical Tests
Sodium Rhodizonate
• Filter paper moistened with 0.1 HCl is pressed against the wound.
• It is then blow dried.
• Spotted with Sodium Rhodizonate paper gives orange colouration
indicating presence of Lead.
• Solution of HCl is then again sprayed until orange colour disappears.
• Gradual appearance of purple spots confirms the presence of Lead.

18. Walker Test
• Photographic paper is desensitised with a hypo fixer and then
immersed in 5% 2-Napthylammine-4,8-sulphonic acid.
• Cloth wetted with 20% Acetic Acid is then placed over the “Sample
Cloth”, on top of which prepared photographic paper is placed and
covered with a dry cloth.
• Warmed and ironed for 5 minutes.
• Bright red colouration gives presence of Nitrite.

19. Marshal Test
• Desensitized photography paper is immersed in 0.5% Sulphanillic Acid and
then dried.
• It is then immersed in 0.5% solution of N-alpha-Napthylethylienediammine
Hydrochloride in Methanol.
• Cloth wetted with 20% acetic acid is placed under the sample clothe and
then on top is placed photographic paper and whole preparation is covered
with a dry cloth and ironed for 5 minutes.
• Purple spots on purple background indicates presence of Nitrites.
• Rinsed in distilled water to remove background colour.
• Immersed in Methanol to give orange colour, confirming presence of
Nitrites.

20. Tewari Test
• 1gm of Antazoline is dissolved in 50ml of distilled water.
• 45ml of conc. HCl is added until white ppt is dissolved.
• Filter paper soaked in Acetone is pressed against wound.
• Air dried and sprayed heavily with the Antazoline solution.
• Bright yellow spots indicate presence of Nitrites.

21. Dermal Nitrate Test
• 0.25% solution of Diphenylamine is sprayed over paraffin cast of
perpetuator’s hands.
• Blue colour indicates presence of Nitrates.

22. Instrumentation Methods
Scanning Electron Microscope
• Scanning electron microscope was first developed by Knoll and
Zworykim in 1942.
• The working principle of the instrument is that a high energy electron
beam is projected upon the surface of the given sample which scans
the sample and image is projected upon a screen (PbS coated)
• It consists of following components.

23. • Electron Gun- usually made up of tungsten
shoots the beam of electron.
• Condenser Lenses- these are electromagnetic
lenses that adjust the illumination or
magnification by altering the velocity of
electrons, by increasing the velocity we
decrease the wavelength thereby increasing its
magnification, resolution and depth of focus.
• Scanning Coils- these are current carrying
metallic coils that alter the movement of
electrons by altering the flow of current through
them.
• Projection Lens- this is the lens which has been
replaced with the eyepiece of a light
microscope.

24. • Detectors-these detect how the electrons interact with the sample.
• Objective Lens- inserted to adjust the aperture.
• Fluorescent Screen- This is where we obtain the final image it is coated
with Lead Sulphide.
Transmission Electron Microscope
• Designed in 1931 by Luska and Max.
• Its working principle is same as SEM just that it requires sample in a form
very thin layer and it is not capable to give a 3D image.
• It is about 1000x times stronger than light electrons.

25. Neutron Activation Analysis
• It is based on the principal that when neutrons are bombarded upon
any substance, a certain amount of radioactivity is induced in that
material.
• The measure of this induced radioactivity can provide qualitative and
quantitative data for that particular material.
• It was developed by Havsi and Levi in 1936 and is also termed as
referee method as it gives reference data for other tests.
• It gives result in the unit of particles per billion.
• Almost 100000 samples undergo NAA each day.

26. Process
• Neutrons are bombarded upon the sample
thereby converting it into a compound nucleus
which is highly unstable.
• Compound Nucleus in an attempt to attain
stability release Prompted Gamma Rays (which
come under PGNAA) and passes through an
intermediate state of being radioactive.
• This radioactive nucleus radiate Delayed Gamma
Rays.
• These Delayed Gamma Radiations come under
DGNAA and 70% of the materials show this
property.
• The energy of DGR is directly proportional to
Radioactivity of the material.
• Curve between energy of Gamma Rays and
Radioactivity is plotted and gives qualitative and
quantitative data.
Target
Nucleus
Compound
Nucleus
Radioactive
Nucleus
Product
Nucleus

27. X-Ray Florescence
• Florescence is a phenomenon in which some materials
absorb low wavelength (UV) Electromagnetic Radiations
and radiate a part of them converted into a spectra of
visible light of various wavelength and colour.
• In case of X-ray fluorescence the incidents X-ray as well
as fluorescent radiation both are invisible to the human
eyes as both the radiation incident and fluorescence lie
in the invisible spectrum, but the basis fact remains the
same meaning thereby that in the incident X-ray
radiation will be of lower wavelength and fluorescence
radiation of higher wave length.
• The sample to be analysed for elemental composition is
placed in the path of X-ray beam which will get absorbed
by the sample. The absorbing atoms get excited and emit
X-ray of characteristic wavelength of elements present in
the absorbing material and this process is known as
fluorescence. As the wavelength of the fluorescence is
characteristic of excited atoms of particular elements,
measure of this wave length would enable one to
identify the fluorescing element.
• For calculating wavelength Bragg’s Law is applied which
is λ = 2 d Sin θ
θ θ
θ θ
d –
Crystal
Lattice

28. Forensic Relevance
• Range Determination.
• Crime Scene Reconstruction.
• Identification of Cartridge and Firearm.
• Identification of Suspect.
• Analysis and linking of secondary evidences (intermediate targets).

29. Thank You.