- 01: Introduction
- 02: History
- 03: Propellants, Firearms, and Ammunition Development
- 04: Modern Firearms Manufacture
- 05: Small Arms Ammunition
- 06: Evidence Handling Procedures
- 07: Equipment and Instrumentation
- 08: Examination of Firearms
- 09: Cartridge and Shotshell Examination
- 10: Characterization and Evaluation of Fired Projectiles
- 11: Bullet Comparison and Identification
- 12: Gunshot Residue and Distance Determination
- Introduction
- Objectives
- AFTE Knowledge and Ability Factors
- Powders and Residues
- Examination
- Distance Determination
- Significance of Results
- Contact Shot
- Nitrite Residues
- Vaporous Lead Residues
- Residues Consistent with the Passage of a Bullet
- Residues Consistent with the Discharge of a Firearm
- Interpretation Challenges
- Reproduction of Results
- Nitrite Residue Patterns
- Shot Patterning
- Chemical Testing
- Shot Pattern Reproduction
- Selected Bibliography
- 13: Toolmark Identification
- 14: Communicating Results
- Resources
Introduction
Home > Gunshot Residue and Distance Determination > Introduction
The use of gunshot residues for determining the distance of the muzzle of a firearm from a target at the time of discharge is a subdiscipline of the forensic firearms specialty. This module covers the examination, testing, reproduction and comparison of residues, and distance determination.
Applying scientific methods, the subdiscipline of using gunshot residues for determining distance is performed in the following manner:
- Testing is conducted only when the suspect firearm is available or per laboratory protocol.
- Visual and microscopic examination is made of evidence items for residues, which may or may not be visible to the unaided eye.
- Testing of evidence items is performed using a sequence of standardized chromophoric (color-producing) chemical tests which are specific for certain metals or compounds typically produced by fired ammunition components, including burned gunpowder.
- Reproduction of these residues in the form of standards fired by the examiner at known distances uses the suspect firearm and ammunition that is as similar as possible to that used in the incident(s).
- Comparison of the residues previously developed on evidence items is made against known standards to determine the distance of a suspect firearm from the target at the time of discharge.
Distance determinations based on gunshot residues are not performed in isolation from the rest of the firearms-related evidence in a shooting case. In summary, this module is directed at acquiring an understanding of the chemical makeup of ammunition propellants, what types of combustion products they produce, and the mechanics of extracting the distance-related information they represent.
