Powders and Residues

Burned or partially burned bullet propellants and other gunshot residues are expelled from the muzzle during the firing process and can be used to determine the distance of a muzzle from a garment or other surface at the time of discharge.

Read more about propellants in Module 03.

When a firearm discharges, the burning of the propellant powder immediately generates a large amount of heat and gas inside the cartridge, providing the pressure required to expel the bullet.

Gunshot residues are composed of the following:

• Primer residues from the combustion of the cartridge priming mixture when the primer was struck by the firing pin
• Residues resulting from the burning of the propellant
• Material generated by the interaction of the bullet with the inside of the barrel
• Unburned and partially burned powder

Examination

When a firearm is discharged and the bullet strikes a surface, gunshot residues are deposited, particularly at close range. These residues may be reproducible and therefore have evidentiary value. Some residues are visible and others require chemical treatment in order to visualize them.

Note:

Evidence should be received and handled according to laboratory protocol.

Read more about evidence handling in Module 06.

Examination Documentation

Visual, microscopic, and chemical examinations should be documented according to laboratory protocol. Written documentation can be supplemented with images of items indicating the presence of physical effects and gunshot residues

   

Click here to read a sample forensic worksheet and report - Gunshot Residue and Distance Determination

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