California Department of Justice Bureau of Forensic Services

Physical Evidence Bulletin

Gunshot Residue (GSR) Collection

Purpose The Physical Evidence Bulletin (PEB) is a guideline intended for law enforcement
agencies to follow in order properly sample, preserve, and to submit gunshot residue
evidence to BFS Laboratories. Physical Evidence bulletins are not intended to be used in
lieu of training in the collection of evidence.

This PEB pertains to sampling and examination for the presence of GSR. For guidelines
pertaining to distance determination, please refer to PEB 12 (Firearms Examination).

Introduction The Bureau of Forensic Services (BFS) provides analytical support to law enforcement
agencies through the examination for gunshot residue. Gunshot residue (GSR) results
from the discharge of a firearm. The residue escapes through openings in the weapon and
the end of a barrel and is deposited on nearby surfaces. The amount of residue detected
varies with the type of weapon, ammunition, conditions of discharge, and post-shooting
activity. GSR analysis does not determine whether or not an individual has
discharged a firearm.

The presence of gunshot residue may occur for the following reasons:
• The individual may have discharged a firearm.
• The surface/individual may have been in the vicinity of a firearm when it was
discharged.
• The surface/individual may have been in contact with a firearm or ammunition.
• The surface/individual may have been in contact with an object or individual bearing
gunshot residue.

The absence of gunshot residue may occur for the following reasons:
• The surface/individual was not in the vicinity of a firearm when it was discharged.
• The surface/individual was in the vicinity of a firearm when it was discharged, but no
GSR particles were deposited on the sampled area.
• GSR particles were removed by washing, wiping, or other activity before the samples
were collected.

PEB 15 (Rev. 8/23/2023) Page 1 of 3

 Sample Some GSR collection kits contain swabs. Please do not use the swabs. BFS is unable
collection to examine swabs and using them before sampling with adhesive discs may remove
GSR particles if they are present.

In order to ensure proper GSR evidence collection, BFS recommends the following:

• Hand samples should be collected immediately after contact with the subject in
the field. To minimize the risk of contamination and/or loss of potential GSR, sample
before handcuffing, transporting, or fingerprinting whenever possible.

• Samples should be collected by an individual who has not recently handled a

firearm. At minimum, the individual collecting GSR samples should wash their hands
prior to collecting the samples and wear the gloves provided in the GSR kit.

• Follow the instructions provided in the GSR kit. Each tube should be properly
labelled to identify the collection surface. A dabbing motion should be used to collect
the sample – do not rub or slide the adhesive across the surface.

Submission All GSR cases must receive BFS approval before submission to the laboratory.
criteria GSR examinations will only be conducted in cases where probative information may be
obtained. Contact your local BFS laboratory to discuss your case prior to submitting any
evidence.

BFS does not examine the following sample types:

• Hand samples collected more than 6 hours after the shooting incident. GSR is
readily shed from the hands during even minor physical activity. The likelihood of
finding GSR after a time lapse greater than 4-6 hours is remote. Sampling for GSR
should be performed as soon as possible after the shooting.

• Samples from a subject who was found in the possession of, or is known to have
recently handled, a firearm. This analysis cannot distinguish between discharging or
handling a firearm.

• Samples from a subject who has washed his/her hands or bathed since the
shooting incident. Washing the hands is likely to remove all GSR.

• Samples from subjects with gunshot wounds or surfaces with bullet impacts. If an
individual (or object) has been shot, then they are known to have been in an
environment of GSR. The absence of GSR also does not rule out the possibility that the
individual handled or discharged a firearm. Additionally, GSR analysis cannot
determine whether a victim’s death was the result of a homicide or a suicide.

PEB 15 (Rev. 8/23/2023) Page 2 of 3

 BFS may examine the following sample types:

• Hand samples (see above for acceptance criteria).

• Clothing or GSR samples from clothing may be accepted if hand samples are not
available and there is a reasonable expectation that the clothing was worn during
the shooting incident and has not been laundered.
− Shirts, sweatshirts, and jackets are preferred. The outermost article of clothing worn
during the incident should be sampled or submitted. Other items of clothing may be
accepted depending on the circumstances.
− Samples of the cuffs/sleeves and front of the garment are preferred.
− Each tube should be labelled with the specific area of the garment that was sampled.

• GSR samples from vehicles may be accepted if hand or clothing samples are not
available.
− The samples should be collected prior to latent print and/or trace DNA evidence
collection.
− Sample(s) of the vehicle headliner are ideal if it is suspected that a firearm was
discharged from within the vehicle.
− Each tube should be labelled with the specific area of the vehicle that was sampled.

Preferred Preferred GSR collection kits contain two stubs with carbon adhesive. The
GSR following manufacturers provide GSR kits with two stubs and other similar kits may be
collection kits acceptable.

• Arrowhead Forensics: https://arrowheadforensics.com

− GSR Kit – SEM 2 Carbon Disks: Part # A-7210-2SB (box) or #A-7211-2SE
(envelope)

• Sirchie: www.sirchie.com
− 2 Stub Forensic Gunshot Residue Field Kit: Product #GRA300

• Tritech Forensics: www.tritechforensics.com

− GSR Collection Kit: Product # GSR-2SEM
− Surface GSR Collection kit: # GSR-SEM/SUR(C)

• Evident: https://www.shopevident.com
− GSR Collection Envelope kit – SEM – 2 Carbon Disks: Product #36542E

For further Please contact your regional BFS laboratory with any further questions that you may
information have.
and additional
resources For a list of regional laboratories please go to:
https://oag.ca.gov/bfs/services

To locate the most current Physical Evidence Bulletins please go to:

https://oag.ca.gov/bfs/peb

PEB 15 (Rev. 8/23/2023) Page 3 of 3