- 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
- 13: Toolmark Identification
- 14: Communicating Results
- Resources
Physical Characteristics
Home > Cartridge and Shotshell Examination > Identification Process > Physical Characteristics
The marks on fired cartridge cases and shotshell cases reflect both class and individual characteristics of striated and impressed toolmarks.
In addition to class and individual marks, there is a possibility for the appearance of a third category of mark - subclass characteristics. These three categories are defined below:
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Extractor, ejector and firing pin aperture
of a Smith and Wesson pistol
- Class characteristics – Measurable features of a specimen that indicate a restricted group source. They result from design factors and are therefore determined prior to manufacture. For purposes of this module, the location, size, orientation, and relationship of the various parts of a firearm are the class characteristics of interest.
- Individual characteristics – Marks produced by the random imperfections or irregularities of tool surfaces. These random imperfections or irregularities are produced incidental to manufacture and/or caused by use, corrosion, or damage. They are unique to a particular tool and distinguish it from all other tools. In the context of this module, the term "tools" refers to the various parts of the action and mechanism of a firearm.
- Note: Accidental characteristics is a term formerly used to mean individual characteristics.
- Subclass characteristics – Discernable surface features of an object that are more restrictive than class characteristics because they are
- produced incidental to manufacture,
- significant because they relate to a smaller group source, that is, a subset of the class to which they belong,
- identifiable within a time frame since manufacturing processes change over time.
Identification of land impressions on bullet
Subclass characteristics should not be confused with individual characteristics. Subclass characteristics are similarities appearing in consecutively manufactured parts of some firearms. These subclass characteristics can reflect the method used by the manufacturer over a particular period of time.
In the case of a "no gun" submission, the influence of subclass characteristics may or may not be eliminated.
Faced with the possibility of subclass influence, the examiner should
- research the manufacturing processes related to a particular make and model,
- consult with peers regarding the firearm in question,
- research pertinent literature, especially the AFTE Journal.
