1. GUN SHOT RESIDUE

2. What is Gun Shot Residue?
Tiny particles of primer and gunpowder (gunshot residue or GSR) are expelled from the front of the gun and from the breechblock area when the gun is fired

3. What is Gun Shot Residue?
The further gunshot residues travel from the muzzle, the broader and less concentrated the pattern becomes. 
Because the various elements included in gunshot residues are very small and lack mass they lose their energy rapidly.

4. How is GSR detected?
Primer is generally made up of barium nitrate and antimony sulfide
Most GSR detection techniques concentrate on barium and antimony
Also lead

5. How is GSR detected? GSR Chemical Tests
Griess Test.
Will not interfere with later tests for lead residues
Detect the presence of nitrite residues
Primary test used by forensic investigators
nitroglycerine

6. How is GSR detected? GSR Chemical Tests
The Griess Test

7. How is GSR detected? GSR Chemical Tests
Sodium Rhodizonate Test
Determines if lead residues are present on the exhibit.
Pink to blue is positive for lead residues

8. How is GSR detected? Entomology
Examiners can extract GSR from the larvae that had been feasting on the body of someone involved in, or that was in proximity to a shooting

9. Can GSR Convict Someone?
All the shooter has to do is wash his hands thoroughly, although normal human movement and activity can dislodge the particles even if he can’t get to a sink
Most labs will not test samples collected more than 6 hours after the shooting
Shooter’s hands are bagged

10. Can GSR Convict Someone?
Barium and antimony can also be found in firecrackers, paint, and some industrial settings
Too many other factors involved—weather (including wind), sweating skin, dry skin, putting hands in pockets, washing

11. Can GSR Convict Someone?
The FBI is no longer analyzing gunshot residue in its investigations
It could become a weapon for defense attorneys in pending cases and in efforts to overturn convictions
May 26, 2006

12. Distance Determinations
GSR on Garments

13. Clothing Distance Determinations
Entrance Holes:
Typically have very even margins
Smaller in diameter than the bullet due to the elasticity of the fabric

14. Clothing Distance Determinations
Holster, the higher the velocity – the more damage to the garment,
Bullet fragments
Bullets shot from an angle has an elongated hole in garment
Angled grazing bullet
Bullet wipe residue – lead from bullet wiped off on garment

15. Clothing Distance Determinations
Exit Holes:
Usually provide no evidence
Usually wider than the actual diameter of the bullet
No bullet wipe residue

16. GSR Deposits GSR travels 3-5 feet in most firearms
At the 3-5 foot range the gunshot residues may only consist of a few trace particles
At around inches most firearms will start to deposit considerable concentrations of GSR
At distances of less than 12 inches heavy concentrations of visible gunshot residues will normally be deposited
Gunshot residue is normally a combination of gunpowder residues and lead residues
Modern – smokeless powder

17. GSR Deposits
GSR is not readily water soluble and clothing left exposed to the elements will not usually diminish the residue deposits
Heavy bleeding & rough handling of the garment can cover up or dislodge some residues

18. GSR Distance Standards
Made by firing the firearm, using ammunition like that used in the actual case, into witness panels that consist of  white pieces of cotton twill jean cloth
Several panels will be fired into at varying distances

19. GSR Distance Standards

20. Ballistic Gelatin
Used by the shooting industry to simulate soft body tissue
Provides an alternative to live animal or cadaver testing.

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