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Gunshot Residue and Distance Determination
retrieved April, 2020
https…
Gunshot Residue and Distance Determination
retrieved April, 2020
https://firearms-examiner.training.nij.gov/
Module 12
Powders and Residues
Burned or partially burned bullet propellants and other gunshot residues are expelled from the muzzle during the firing process and can be used to determine the distance of a muzzle from a garment or other surface at the time of discharge.
Examination
When a firearm is discharged and the bullet strikes a surface, gunshot residues are deposited, particularly at close range
Examination Documentation
Visual, microscopic, and chemical examinations should be documented according to laboratory protocol.
Visual and Microscopic Examination
The preliminary visual and microscopic examinations of gunshot residues should be given first priority because subsequent chemical testing can dislodge residues or alter the appearance of physical effects.
Modified Griess Test
chemically specific chromophoric (color-producing) test for the presence of nitrite compounds, such as those produced by the burning of smokeless powder.
series of chemical reactions result in the conversion of any nitrite compounds that may be present on an item
- Confirm nitrite sensitivity of test paper.
- Mark reference points of evidence on test paper
- Create layers of reaction items
- Heat reaction layers
- Examine and interpret the results
- Label and retain test paper
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Dithiooxamide Test
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Copper is used in:
- Military and sporting jacketed bullets fabricated from gilding metal (a 90/10 copper/zinc alloy) or commercial bronze (a 95/5 copper/tin alloy)
- Rimfire bullets coated or plated with copper or brass (a 70/30 copper/zinc alloy)
- Revolver bullets with copper jackets
- Nickel-plated bullets, e.g. Silvertip bullets
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reagents and test media are required:
- Dithiooxamide
- Ethanol
- Concentrated ammonium hydroxide
- Distilled or deionized water
- White filter paper
- Known source of copper
- Cotton swabs
- Eye dropper bottle
Sodium Rhodizonate Test
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- questioned area is sprayed directly
- buffer solution (pH 2.8) is then sprayed on the area
- dilute solution of hydrochloric acid is applied
Reagents and Test Media
- Saturated solution of sodium rhodizonate dissolved in distilled or deionized water
- Buffer solution of 2.8 pH consisting of sodium bitartrate and tartaric acid in distilled or deionized water
- Solution of hydrochloric acid (5 percent) in distilled or deionized water
- A known source of lead
Bashinski Transfer
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carried out as:
- Position the area to be tested
- Place a test mark on the filter paper
- Prepare the filter paper
- Lift residues from item
- Perform color test
- Label and retain test paper
Distance Determination
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Positive results are duplicated to create known standards by firing the evidence firearm and ammunition at test targets under controlled conditions
Significance of Results
- conclusions must be given as a result of the presence of residue(s)
- absence of gunshot residue cannot be used as a basis for distance determination
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Nitrite Residues
As the muzzle-to-target distance increases, the presence of nitrite residues becomes more important in determining distance
Vaporous Lead Residues
characteristically deposited at closer ranges. These deposits are chemically detectable by an application of the Sodium Rhodizonate Test.
Residues Consistent with the Passage of a Bullet
Holes found in objects, such as garments, with no accompanying particulate residues may appear consistent with the passage of a bullet
Residues Consistent with the Discharge of a Firearm
discharge of a firearm will result in the deposit of particulate lead around a bullet hole
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Nitrite Residue Patterns
known-distance targets should be fired to produce patterns both smaller and larger than the evidence residue patterns