Laboratory methods for firearms evidence

There are a number of questions regarding firearms and ammunition components that the firearms examiner can potentially answer.

• Has the gun been damaged or modified?

• Is there evidence of recent firing on or in the gun?

• Did the gun fire the ammunition components (cartridge case or bullet) that were also submitted with it?

• How far from the target was the gun when it was fired?

Operability testing begins with a visual inspection of the weapon and hand cycling of the action. For a revolver this means cocking the hammer and pulling the trigger to see if the weapon appears to be functioning properly. If the weapon is double action (that is, pulling the trigger both cocks the hammer and fires the weapon), the examiner pulls the trigger while observing the cylinder to see that it rotates. The hammer is also observed to see that it cocks.

It is also possible to insert a wooden dowel rod into the barrel with one end against the firing pin opening. With the barrel pointed straight up to keep the dowel rod against the firing pin opening in the breech face, the trigger is pulled. If the firing pin is functioning properly, the rod can be observed to rise upon impact by the firing pin. The idea is that if there is enough impact force to visibly move the dowel rod, then a cartridge could be fired. This method allows the examiner to determine quickly operability without having to fire a weapon. It also saves expenses on ammunition and lessens the examiner's exposure to noise and vaporous residues.

For semiautomatic weapons operability questions include whether the weapon will eject fired cartridge cases and reload as designed by the manufacturer. For this testing the weapon must actually be fired. From a purely legal standpoint, however, it is only necessary that a weapon be capable of firing a single round in order for it to qualify as a firearm.

If a weapon appears to be potentially unsafe, the examiner can set it up in a fixture that will hold it securely. The examiner then ties a string to the trigger and stands behind a protective barrier so that the weapon

A homicide victim was found to have two bullet wounds at autopsy. The suspect's weapon was a small, cheaply made 22-caliber revolver. Inspection of the contents of the revolver cylinder indicated that there were two fired cartridge cases. However, the location of the two fired cartridge cases was out of sequence. The cylinder rotated clockwise as the weapon was fired, but there was a fired cartridge case under the hammer and a second fired cartridge case two spaces counterclockwise from the first.

When the firearms examiner inspected the bullets recovered from the victim's body at autopsy, he noted that one of the two bullets was devoid of rifling marks. He also noted that the autopsy report described one of the entry wounds as being "irregular" and "suggestive of having struck an intermediate target." An inspection of the fired cartridge cases told the story of what had happened. The cartridge case that appeared out of sequence relative to the one found under the hammer had an uncharacteristic indentation in the rim: It did not have a firing pin impression consistent with this weapon. Examination of the revolver revealed that the cylinder was loose in the frame of the revolver and was capable of sliding back and forth approximately 3 mm.

Under interrogation the suspect finally admitted to having fired one round at the decedent. Although participants often cannot accurately remember the actual number of shots fired in a shooting incident, in

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