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Firearms Examiner Training

Module 11: Bullet Comparison and Identification

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illustration of a gun being fired
National Institute of Justice (NIJ) (see reuse policy).


Author: John H. Dillon, Jr.
Headshot of Author John H. Dillon, Jr
National Institute of Justice (NIJ) (see reuse policy).
Jack Dillon earned a B. S. from the United States Naval Academy and an M. Ed. from the University of Virginia. Commissioned in the United States Marine Corps in 1964, he attained the rank of Captain of Marines. Appointed a Special Agent, FBI, in 1970, he investigated diverse criminal violations, including organized crime, bank robberies, extortions, and kidnappings. In 1976 he received orders to the Firearms/Toolmarks Unit of the FBI Laboratory for training as an examiner, where he evaluated evidence and provided on-site field support in domestic cases, as well as abroad. He also designed and taught basic and management-level forensic courses at the FBI Academy, Quantico, Virginia, 1982-1988. Jack retired from the FBI as Chief of the Firearms/Toolmarks Unit in 1994, and continues to consult in forensic firearm cases and in training design and delivery.



The comparison and identification of fired bullets as having been fired from a particular firearm is the most important type of examination in the field of forensic firearms. This technique is performed when two bullets bear consistent general rifling characteristics (GRCs). This module introduces the student to the basic techniques used to perform bullet comparisons at the microscopic level.

In summary, this module addresses the essential request made of a firearm examiner: Was this bullet fired by this firearm?, and provides the basis for answering it to the extent allowed by the physical evidence.


At the conclusion of this module the student will be able to do the following:

  • Define the following concepts as they relate to the formulation of conclusions:
    • Class characteristics
    • Individual characteristics
    • Subclass characteristics
    • Pattern matching
    • AFTE Theory of Identification
    • Sufficient agreement
    • Best known nonmatch
    • Consecutive matching striae (CMS)
    • AFTE Range of Conclusions
  • Explain the differences between the following terms in regard to comparisons of bullets:
    • Identification
    • Inconclusive
    • Elimination
    • Unsuitable
  • Describe the examination protocol for the microscopic comparison of the individual characteristics of fired bullets
  • Define the contents of a typical bullet comparison worksheet for documentation of examination notes
  • Discuss typical formats and content for reporting of results of fired bullet comparisons in terms of the conclusion categories
  • Discuss in general terms the Integrated Ballistics Identification System (IBIS) in regard to preliminary remote comparisons (computer correlations) and case linkage
  • Describe the rationale and procedures for replicating the surfaces of fired bullets using casting materials


AFTE Knowledge and Ability Factors

14. Knowledge of how to properly document evidence and analytical results (through notes, sketches, photography, reports, etc.)
15. Knowledge of the techniques and procedures used to properly mark evidence (when appropriate)
26.* Knowledge of definitions of class, subclass, and individual characteristics and the differences between them
27.* Knowledge of the sources of class, subclass, and individual characteristics
116.* Knowledge of the interactive nature of the tool/toolmark process and the transference of class, subclass, and individual characteristics
117. Knowledge of impressed (static) vs. striated (dynamic) toolmarks
118. Knowledge of the best agreement possible in situations of known nonmatches when comparing toolmarks
119. Knowledge of the principles of preparing test marks and the effects of test materials in the production of testfired cartridge components and toolmarks for comparison
4. Ability to select the appropriate casting materials (casting of bullets/toolmarks)
17. Ability to select proper casting material and technique
19. Ability to understand and interpret technical data output from laboratory instruments
21. Ability to recognize discrepancies or inconsistencies in analytical findings and determine their cause and significance
23. Ability to recognize the limitations of tests and interpretations
30. Ability to recognize the effect that firearms and ammunition manufacturing processes, the design of firearms, and design of firearms accessories have on markings imparted to bullets and casings and to interpret them accordingly
31.* Recognize different manufacturing methods and, based upon this, to properly interpret potential for class, subclass, and individual characteristics
34. Ability to distinguish action markings from those caused during firing (action markings meaning mechanism marks)
40.* Ability to recognize manufacturer-induced/placed toolmarks (subclass characteristics) on ammunition as well as their usefulness and limitations
46. Ability to recognize (1) those attributes or characteristics of a particular firearm design which are reflected in the fired projectiles and fired cartridge cases and (2) nonfirearm-caused toolmarks on ammunition components
47. Ability to determine the source and uniqueness of various striated and/or static marks on bullets and cartridges
48. Ability to recognize and properly align reproducible striae arrays sufficient for identification purposes
49.* Ability to recognize, determine the source of, and differentiate between class, subclass, and individual characteristics on bullets, cartridges, cartridge cases, and in nonfirearm-related toolmarks
50. Ability to make comparisons between evidence and reference cartridges and recovered cartridge components
53. Ability to distinguish between the quality and quantity of matching striae in a true identity and that observed in known nonmatches
57. Ability to recognize any manufacturer-induced characteristics
71. Ability to make determinations in toolmark comparisons (both firearm and nonfirearm toolmarks) regarding identifications, exclusions, and inconclusives
72. Recognize patterns (profiles, etc.) produced by various tool working surfaces
73. Ability to recognize sources of class, subclass, and individual characteristics on any given tool
74. Ability to recognize toolmarks as being class, subclass, or individual in nature
* Module 9 includes information on class, subclass, and individual characteristics in regard to cartridge cases. Module 10 includes class characteristic information on fired and unfired bullets, and Module 11 includes information on subclass and individual characteristics in regards to fired bullets

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