Firearm examiners perform testing to determine the functioning ability of a firearm. The examiner wants to answer the question "Is the firearm in an operational condition that it could have malfunctioned (failed to fire or fired unintentionally) during the time of the incident in question?"
Examiners may evaluate and test a firearm’s mechanical condition and observe if any modifications were made to the firearm. For example, examiners can recognize a semi-automatic rifle that contains machine gun parts. This modification causes the rifle to fire full-automatic, creating an unsafe condition and rendering the firearm illegal.
Firearm examiners may use reference firearms as samples when diagnosing function problems on an evidence firearm. The examiners can also use the reference firearms to supply missing or damaged parts to non-functional evidence firearms so they can create test specimens