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John H. Dillon, Jr. “Module 12: Gunshot Residue and Distance Determination…
John H. Dillon, Jr. “Module 12: Gunshot Residue and Distance Determination.” Firearm Examiner Training, National Forensic Science Technology Center, projects.nfstc.org/firearms/module12/fir_m12.htm.
Powders and Residues
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Composed of residues from primer, propellant, powder, and the barrel of the firearm
Examination
Visual and Microscopic Examination: perform preliminary examination with bare eyes or stereomicroscope, looking for gunpowder, burned fibers on the tip, and more
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Distance Determination
Interpretation Challenges: rough handling, weather, blood, temperature, and unburned ball powder can all present challenges to interpretation
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Residues Consistent with the Discharge of a Firearm: the residues aren't reproducible and therefore pretty much useless
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Nitrite Residue Patterns: reproduce from one distance where gunpowder is always found and one distance where gunpowder is never found for a reliable range
Vaporous Lead Residues: sodium rhodizonate can also be used to determine distance or corroborate the modified griess test
Shot Patterning: can help in distance determinations with firearms with pellets, like shotguns
Nitrite Residues: used modified greiss test to determine distance of the shot due to nitrite residues around bullet holes
Chemical Testing: performed even on shot patterns to determine whether not a bullet was fired as well
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Shot Pattern Reproduction: shot patterns can vary, so it is based off of the diameter of the spray
Significance of Results: the results of the three tests must be in agreement for the results to be significant