This document discusses the examination process for firearm evidence. It explains that firearms evidence is examined when a weapon has been discharged at a crime scene. Examiners can identify or eliminate firearms as being involved through comparison of cartridge cases, bullets, or the firearm itself if available. Tests are conducted by discharging ammunition through the firearm and recovering test bullets and cartridge cases to compare with evidence. Multiple techniques are used in the comparison process like stereomicroscopy, comparison microscopy, and scanning electron microscopy. The document also provides details on unique issues with examining homemade or improvised firearms.

1. Unit 5: Firearm Evidence
Dr. Shayani Ghosh
Assistant Professor
Kristu Jayanti College

2. Why and when is firearms evidence
examined?
• Firearms evidence can usually be found at any crime scene where a weapon has been fired.
• When evidence such as shot shell casings, cartridge cases, bullets and slugs is found at a
crime scene—or recovered from victims, buildings, furniture, vehicles, trees, etc.
• When a firearm is recovered, the examiner can either identify or eliminate it as the firearm
used in the crime, provided that
(1) it still fires and
(2) there is evidence such as a cartridge case or bullet for comparison.
• In addition, GSR, powder burns

3. test Exhibit
• The identification of firearms ammunition is carried out by comparison with test exhibits
• A number of test Cartridges are fired in such cases before the acceptable test exhibit is
obtained
• The ammunition of same make and batch is used for test firing.
• In defective, damage firearms, charge of the cartridge is reduced before it is fired for test
purposes

4. test Exhibit
• If firearms cannot be used for test firing, then cast of the relevant part is made in a suitable
medium.
• Materials : Lead, silicon rubber, etc.

5. Test bullets
• Materials such as rags, paraffin, soap have been used in test firing to obtain
test bullet.
• Bullet recovery box: Divided into compartments, separated by filter paper
sheets.
• Compartments are filled with clean cotton
• There is a lid at the top which is lifted when the bullet is to be located in the
box after firing
• One side is open, forming front face of the box

6. • Bullet recovery box:

8. Bullet recovery Water tank
• typically oriented horizontally and measured approximately ten feet long and five feet
high
• Water filled the tank to just below the firing port
• firing port angled to facilitate shooting diagonally from the top edge of one end of the
tank to the bottom of the opposite end
• bullet should travel a minimum of ten to twelve feet on the diagonal

10. Test marks from smooth bore
• Basic requirement is that the projectile should carry marks from the whole surface of
the barrel
• Achieved by pushing a tight fitting slug made of lead through the barrel without
circular motion
• Slug carries all the marks of bore surface of the barrel

11. Test marks from smooth bore
By examining wadding materials, the examiner may be able to determine
• the gauge of the shotgun
• the manufacturer or marketer
• A range of possible shot sizes based on impressions in the shot shell wad
• individual characteristics (in some cases)

12. Examination
Physical Examination:
• Cleaned
• Visual examination: Position and size of firing pin, breech face, other marks
• Gross characteristic indentation, allows elimination of suspected exhibit
• Cliber, no. of L&G, depth, width, direction

13. Examination
Stereomicroscope:
• Three dimensional image
• Perception of depth is better
• The cartridge case examination by Stereo microscope is very much superior analysis

14. Comparison microscope
• Side by side analysis
• Two microscopes connected by an optical bridge, enabling two objects to be viewed
simultaneously
• Optical bridge consist of a series of lens and mirror that brings two images together
under a single eyepiece
• A line in the middle separate the view field into two parts

15. Comparison microscope
• The images from the comparison instrument can also be transferred to a computer monitor, television
screen or sent via the Internet to a remote computer.
• Philip O. Gravelle developed the comparison microscope for the identification of
fired bullets and cartridge cases with the support and guidance of Major Calvin H. Goddard.

16. Comparison microscope
• Side by side
• Composite
• Superimposition techniques: The dividing line bisects the two images exactly in the
field of view such a way that when the dividing line is moved to one side slowly the
below image can be seen to match exactly the above image

18. Scanning Electron Microscope
A beam of the electrons is impinged on the surface. The extent, direction and intensity of
secondary electrons emitted by the surface depends of the questioned surface area and the
original beam.
• Examination of all sort of microscopic surface characteristics
• Examination of marks on fired ammunition (pin marks, extractor marks, ejector marks, marks
on bullet
• Examination of GSR, gunshot injuries, range of fire
• Scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDX), trace
deposits on the discharged bullet and the intermediate target,

19. Striagraphy
Study and compare the striations found on bullets: Striagraphy
• A very fine stylus, tip diameter <0.0002 cm, rest on a bullet
• The bullet slowly rotates slowly at the rate of one-tenth revolution per minute
• The angular speed is synchronized with the angular speed of drum carrying the chart
paper
• The tip of the stylus moves up and down according to the striations on the surface of
bullets
• Up-and-down movement is amplified and recorded on a graph paper

20. country made firearms

21. country made firearms
• Improvised Firearms, home-made forearms, zip guns, pipe guns, etc.
• Made illegally, improvised by culprits from readily available materials
• Non-standard, non-tested, non-worthy
• Classification: reference to ammunition used in them
according to the manner in which they are fired
• They are largely smooth bore barrels

22. country made firearms: Usual Parts
• Barrel:
The diameter of the bore/caliber may not corresponds to that of a standard firearms
The bore surface is never smooth
Thickness of barrel wall differs from one firearm to another
Loose and non-uniform barrel
The bore of the barrel can be oversized, undersized, same size with respect to the bullet

23. country made firearms: Usual Parts
• Chamber:
Doesn’t have specially made chamber, barrel ends serves as chamber
Sometimes the bore diameter is more than the base diameter
Don’t have proper dimensions, no proper arrangements for seating cartridge
correctly
Loose chamber causes cartridge burst

24. country made firearms: Usual Parts
• Action:
Hammer is cocked manually
Firing pin is more or less a headless nail
Often longer than needed and can pierce the percussion cap
Backward leakage of gases
Unique impact of base and sides of case
In some cases, firing pin continues to be pressed against the case as there is no spring
action to take it back

25. Evaluation
• Cartridge-firearm linkage
• Bullet-firearm linkage
• Buckshot-firearm linkage
• Wad-firearm linkage

26. Evaluation
• Power charge needs to be reduced
• Jammed bullet or cartridge cases can be cocked manually with the help of a hammer
• Imprinting the damaged part of the firearm part with suitable materials like Plasticine,
Kerr’s Dental mass, cellulose acetate solutions
• Bullets can be pushed through the barrel with great force, if firing pin, or cocking
mechanism doesn’t work
• Smoke may deposit in cushion wads, may carry irregularities of the barrel