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Chemical Testing

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Chemical Testing

As in the case of performing the chemical processing of suspected bullet holes, processing shot patterns employs the same procedures with a few additional considerations. The Modified Griess Test and the Sodium Rhodizonate Test are performed because a shot pattern may conceal a bullet hole and other residues. The presence of pellet wipe and the lead randomly deposited by the impact of wadding materials would be apparent as a result of testing.

Although it may be possible to detect vaporous lead and nitrite residues as a result of a shotgun discharge at closer ranges, it is typically the shot pattern that is the determining factor for distance.

Shot Pattern Reproduction

Shot patterns produced using the same 12-gauge shotgun with shotshells containing #4 shot pellets
Shot patterns produced using the same 12-gauge shotgun with shotshells containing #4 shot pellets
Courtesy of Jack Dillon (see reuse policy).

The reproduction of shot patterns, as noted in the gunshot residues section, should employ the same shotgun and type of ammunition as used in the incident, per laboratory protocol. If a shotgun has a variable choke, the reproduction of shot patterns should be conducted with the firearm in the same condition as when it was received in the laboratory. Indexing the choke and barrel with a scribing tool prior to firing provides future reference.

A box of shotshells will produce shot patterns that may vary noticeably when used in the same firearm. Therefore, the same diameter of shot pattern may be produced at a number of different distances within a span of varying ranges. To develop a distance determination range, it is necessary to determine at what range a known-distance pattern is always smaller than an evidence pattern and at what range the known pattern is always larger.

At greater distances, stating a larger range is appropriate. For example, if testing yielded data that supported a firing distance of approximately thirty feet, a reasonable range for distance determination would be twenty-five to thirty-five feet. If the firing distance is shorter, for example approximately twenty feet, the range would be stated at seventeen to twenty-three feet. After the examiner tentatively establishes the extremes of the range, each extreme should be verified by a number of firings to ensure reliability.

Selected Bibliography

The Selected Bibliography is a list of the writings that have been used in the assemblage of the training program and is not a complete record of all the works and sources consulted. It is a compilation of the substance and range of readings and extensive experience of the subject matter experts.

  1. Allen, D.E. 1983. Effects of blood on gunshot and gunpowder residue. AFTE J 15 (2): 102.
  2. Bashinski, J.S, J.E. Davis, and C. Young. 1974. Detection of lead in gunshot residues on targets using the sodium rhodizonate test. AFTE J 6 (4): 5.
  3. Bonfanti, M, and A. Gallusser. 1995. Problems encountered in the detection of gunshot residues. AFTE J 27 (2): 105-122.
  4. Branch, D.M. 1982. Possible greiss test contamination. AFTE J 14 (3): 1.
  5. Brown, C.G. 1985. Detection of nitrites and lead in gunpowder residue patterns. AFTE J 17 (2): 118.
  6. Chaklos, D., and A. Davis. 2005. Visualization of gunpowder residue patterns using a digital infrared camera and optical filters. AFTE J 37 (2): 117-122.
  7. Davis, T.L. 1972. The Chemistry of Powder and Explosives. Las Vegas: Angriff Press.
  8. Denio, D.J. 1997. Forms to document procedure in case notes: Chemical tests for gunshot residues. AFTE J 29 (1): 61-65.
  9. Dillon, J.H. 1989. Graphical analysis of the shotgun/shotshell performance envelope in distance determination cases. AFTE J 21 (4): 593-594.
  10. Dillon, J.H. 1990. Modified griess test: A chemically specific chromophoric test for nitrite compounds in gunshot residues. AFTE J 22 (3): 243-250.
  11. Dillon, J.H. 1990. Sodium rhodizonate test: A chemically specific chromophoric test for lead in gunshot residues. AFTE J 22 (3): 251-256.
  12. Dillon, J.H. 1990. Protocol for gunshot residue examinations in muzzle-to-target distance determinations. AFTE J 22 (3): 257-274.
  13. Dillon, J.H. 1991. Protocol for shot pattern examinations in muzzle-to-target distance determinations. AFTE J 23 (1): 511-521.
  14. Dillon, J.H. 1991. Manufacture of conventional smokeless powder. AFTE J 23 (2): 682-688.
  15. Doyle, J.S. 1987. Griess test modification. AFTE J 19 (2): 165-168.
  16. Fiegl, F. 1966. Spot Tests in Organic Analysis. 7th Edition. New York: Elsevier Publishing Company.
  17. Fiegl, F. 1972. Spot Tests in Inorganic Analysis. 6th Edition. New York: Elsevier Publishing Company.
  18. Garrison, D.H. 1995. Field recording and reconstruction of angled shot pellet patterns. AFTE J 27 (3): 204-208.
  19. Haag, L. 1994. Gunshot residue testing of bloody garments. AFTE J 26 (2): 155-156.
  20. Haag, L. 2001. Method for improving the griess and sodium rhodizonate tests for GSR patterns on bloody garments. AFTE J 23 (3): 808-815.
  21. Haag, L. 2001. The sources of lead in gunshot residue. AFTE J 33 (3): 212-218.
  22. Haag, M.G. 1997. 2-Nitroso-1-naphthol versus dithiooxamide in trace copper detection at bullet impact sites. AFTE J 29 (2): 204-209.
  23. Hueske, E.E. 1994. Gunshot residue testing of blood stained garments. AFTE J 26 (1): 26-33.
  24. Lindman, D.A. 1989. Weathering time factor in GSR proximity determinations. AFTE J 21 (3): 500-502.
  25. Malikowski, S.G. 2003. Alternative modified griess test paper. AFTE J 35 (2): 243.
  26. Shem, R.J. 2001. A simplified griess and sodium rhodizonate test. AFTE J 33 (1): 37-39.

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