Module 08: Examination of Firearms

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illustration of a gun being fired

Photo of William Conrad

Introduction

This module discusses some of the most common types of firearms that an examiner might receive as evidence. The techniques presented can be adapted to any firearm. New models, variations of old models, and new designs are constantly introduced to the firearms marketplace, requiring the firearm examiner to continue to research and study new products.

Many people are exposed to the misuse of firearms through personal experience and misunderstandings. The firearm examiner must overcome misconceptions, and understand and be able to explain the type of firearm, its capabilities and limitations, and how this information correlates with the facts of the case.

The firearm examiner must be able to do the following:

Classify firearms
Determine operability
Explain the safety features of the firearm and their proper function

In addition, having an understanding of how a particular firearm functions allows the examiner to determine what type of identifiable microscopic marks may be present on submitted bullets and cartridge cases.

The quality assurance officer or appointed individual will do an administrative and technical review of the results of the examination and attest that the protocols have been adhered to throughout.

Objectives

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

Explain the cycle of fire for manufactured firearms
Describe the evidence documentation required prior to the examination
Identify the type, caliber, action, and safety features of firearms through visual examination
Know how to conduct a safety and functionality examination of a firearm before conducting test fires
Describe how a firearm functions, including its capabilities and limitations
Describe safety features of firearms and how they function or are determined to be nonfunctional
Describe the methods of test firing a firearm including full automatic, single-action, and double-action type firearms
Describe how to perform a drop test

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)
38.	Knowledge of how and when to use various vises, clamps, and restraining devices
39.	Knowledge of how and when to use gunsmithing tools
43.	Knowledge of how and when to use borescopes
44.	Knowledge of how and when to use bore lights
70.	Knowledge of how and when to use spring trigger pull scales
71.	Knowledge of how and when to use trigger pull weights
76.	Knowledge of breech-loading firearms designs, including falling breechlocks, bolt actions, lever actions, pump actions, break open, semiautomatics (blowback, gas operated, recoil operated, etc.), revolvers--double and single action
77.	Knowledge of firearms ignition systems: flintlock, percussion, rimfire, centerfire, caseless ammunition
80.	Knowledge of sources of information regarding identification markings and serial numbering systems in firearms (including locations of serial numbers, part/assembly numbers, proof marks on firearms and the locations of hidden numbers)
81.	Knowledge of the proper operation of the different types of firearms encountered in casework
82.	Knowledge of the different materials that may be present in the bore of a firearm
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
22.	Ability to recognize utility and limitations of reference collection/database programs
23.	Ability to recognize the limitations of tests and interpretations
24.	Ability to determine the design of the lockwork (firing system) in firearms
25.	Ability to locate and identify the type (or types) of safety system(s) incorporated in a particular firearm
26.	Ability to determine the design type, method of operation, and ignition of a submitted firearm
27.	Ability to recognize when a firearm has been altered from its original design
32.	Ability to examine, either directly or through the use of casts, the interior surface of a gun barrel to determine the method of rifling
35.	Ability to evaluate the operability of each safety system, chambering method, and lockwork, recognize and explain any defects or failures in each of these systems and the consequences of any such defect or failure
36.	Ability to compare firearm mechanisms with standards
37.	Ability to recognize which parts of a firearm leave tool marks of forensic interest