Standard Practice for Expert Opinions 

on the Interpretation of Primer 

Gunshot Residue (pGSR) Analysis by 

Scanning Electron Microscopy/Energy 

Dispersive X-Ray Spectrometry 

Gunshot Residue Subcommittee

Chemistry Scientific Area Committee

Organization of Scientific Area Committees (OSAC) for Forensic Science 

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OSAC Proposed

Standard Practice for Expert Opinions on the Interpretation of

Primer Gunshot Residue (pGSR) Analysis by Scanning Electron

Microscopy/Energy Dispersive X-Ray Spectrometry

Prepared by 

Gunshot Residue Subcommittee

Version: 1.0 

March 2020 

Disclaimer: 

This document has been developed by the Gunshot Residue Subcommittee of the Organization 

of Scientific Area Committees (OSAC) for Forensic Science through a consensus process and 

proposed for further development through a Standard Developing Organization (SDO). This 

document is being made available so that the forensic science community and interested parties 

can consider the recommendations of the OSAC pertaining to applicable forensic science 

practices. The document was developed with input from experts in a broad array of forensic 

science disciplines as well as scientific research, measurement science, statistics, law, and 

policy. 

This document has not been published by a SDO. Its contents are subject to change during the 

standards development process. All interested groups or individuals are strongly encouraged to 

submit comments on this proposed document during the open comment period administered by

ASTM International (www.astm.org). 

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Standard Practice for Expert Opinions on the Interpretation of Primer Gunshot Residue (pGSR) 

Analysis by Scanning Electron Microscopy/Energy Dispersive X-Ray Spectrometry 

1. Scope

1.1 This document applies to persons who present expert opinions regarding primer gunshot

residue analysis results.

1.2 This document defines the range of opinions that are based upon the existence of a body of

published scientific literature. This document does not address all possible circumstances that

may be encountered when giving an expert opinion.

1.3 This document cannot replace knowledge, skill, or ability acquired through appropriate

education, training, continued competency, and experience. It should be used in conjunction with

professional judgment.

1.4 The use of this document presumes that the data on which an opinion is being offered was

obtained under requirements of ASTM E1588 or a comparable published standard.

2. Referenced Documents

2.1 ASTM E1588, Standard Practice for Gunshot Residue Analysis by Scanning Electron

Microscopy/Energy Dispersive X-Ray Spectrometry, ASTM International, West Conshohocken,

PA, 2017, www.astm.org. (1)

3. Terminology

3.1 See ASTM E1588

3.1.1 The term “pGSR”, when used in this document, refers to particles that are classified 

as characteristic of primer gunshot residue as defined in ASTM E1588. 

3.2 OSAC Lexicon 

4. Significance and Use

4.1 This document is of use to persons who present expert opinions regarding primer gunshot

residue analysis results and to provide guidance to those in the legal community who use such

opinions.

5. Procedure:

5.1 The following topics address a broad range of primer gunshot residue related knowledge.

Statements made regarding the following and any additional topics regarding primer gunshot

residue must be based on scientific studies and literature with broad community acceptance,

published literature and relevant experience in the field.

5.2 Formation

5.2.1 pGSR particles are created by rapid heating and chemical transformation of the 

components of the ammunition during the discharge of a firearm, followed by the rapid 
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dispersal of these components in the gases escaping from the firearm, and the rapid 

cooling of these materials to the point of solidification. (4)

5.2.2 Most of the materials that are incorporated into pGSR particles are derived from the 

primer of the ammunition, along with materials from the projectile and the cartridge case.

5.2.3 The process of pGSR formation does not yield specific ratios of each of the elements in 

the original primer. Instead, there is chaotic mixing that produces a wide range of 

component ratios among particles produced in a single discharge. Elemental composition 

may vary from area to area within a single particle.

5.2.4 There is a great range of overlap in compositions of particles produced by different 

ammunitions that use similar formulations for their primer.

5.2.5 The residues that are released from a firearm during discharge can incorporate elements 

that have been left behind on the interior of the firearm from a previous discharge, leading 

to a mixture of particle compositions being emitted. (5)

5.2.6 The identity of the specific ammunition from which a given pGSR particle was generated 

cannot be definitively determined. However, a comparison between the composition of 

the pGSR found on a sample source and that in the spent ammunition can be used to 

conclude that the ammunition could be or could not be the source of the pGSR.

5.2.7 The identity of the specific firearm from which a given pGSR particle was generated, 

including the type, manufacturer, and caliber, cannot be determined by pGSR analysis. 

5.2.8 In general, the morphology of pGSR particles is spheroidal and does not have a crystalline 

appearance. The majority of pGSR particles detected are >1 μm in diameter. However, 

size and morphology can vary greatly and should not be the primary criteria for 

identification. 

5.2.9 There is no means of determining when a given pGSR particle was formed.

5.3 Deposition of pGSR

5.3.1 pGSR that is airborne can deposit on a person or item that is present. (6)

5.3.2 The deposit of pGSR particles is impacted by environmental conditions. Such 

factors that affect deposit of pGSR include proximity, weather, air flow, humidity, 

and indoor versus outdoor environments.

5.3.3 pGSR particle deposit in controlled conditions occurs in the proximity of a 

discharged firearm. (7)

5.3.4 The specific distance that an individual or object was located from a firearm at the 

time of discharge cannot be determined from the pGSR findings.

5.3.5 The direction or angle that a firearm was pointed during discharge cannot be 

determined.

5.3.6 The relative likelihood of a particular deposition method cannot be determined. (8)
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5.4 Transfer 

5.4.1 pGSR can be transferred from one surface to another by physical contact. (2)

5.4.2 The nature of the surfaces that are in contact with each other (texture, 

presence/amount of contaminant material) can impact the degree of pGSR transfer. 

(9)

5.4.3 The specific rate of transfer cannot be determined or calculated.

5.4.4 The time of transfer cannot be determined.

5.5 Retention/Persistence

5.5.1 pGSR removal is dependent upon:

5.5.1.1 pGSR particles may be removed from surfaces through physical contact

5.5.1.2 Type of physical activity. (9)

5.5.1.3 Level of physical activity, frequency and degree of contact with other 

surfaces. (7)

5.5.1.4 Nature of the surfaces (the retaining surface, the removing surface, and 

surface orientations).

5.5.1.5 Exposure of the GSR bearing surface to liquids.

5.5.1.5.1 Washing /showering. (7)

5.5.1.5.2 Exposure to inclement weather conditions.

5.5.1.5.3 Blood / body fluid loss.

5.5.2 If undisturbed, pGSR particles can remain indefinitely, such as on stored clothing.

5.5.3 The number of confirmed pGSR particles cannot be used to determine the time of 

a shooting or an individual’s involvement in a shooting event.

5.6 Specificity/Other Sources 

5.6.1 Other uses of explosive primer material exist and can generate pGSR particles with 

elemental indicators. (10)

5.6.2 Firearm discharges produce particles comprised of combinations of two of the 

three elements: lead, barium and antimony. Sources of these particles other than 

firearms discharges have also been confirmed. Such particles are found in primer 

residue, but also may originate from other sources. (6)

5.6.3 Statements may be made regarding particles not considered pGSR in relation to 

specific and unusual ammunition with reference to a scientific study or published 

literature accompanying the conclusions. Limitations of potential non-firearm 

sources must be clearly noted.

5.6.4 Particles comprised of a single element may be generated from a firearm 

discharge; however, there are many non-firearm sources of these particles. In 

isolation such particles have little use for interpretation of GSR results in the 

absence of a reference sample.
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5.7 Clothing/Vehicles/Inanimate Objects

5.7.1 The presence of pGSR on a garment does not provide any information about who 

was wearing the garment during a shooting event.

5.7.2 The time pGSR is deposited on an inanimate object cannot be determined.

5.7.3 It cannot be determined whether deposited pGSR is from a primary, secondary, or 

tertiary transfer.

5.8 Overall Conclusion Based on the Confirmation of pGSR.

5.8.1 The presence of pGSR on a person is the result of one or more of the following

actions: (11)

5.8.1.1 Discharge of a firearm.

5.8.1.2 Being in the vicinity of a firearm discharge.

5.8.1.3 Coming into contact with a surface or exposure to an environment bearing 

pGSR.

5.8.2 The number of confirmed pGSR particles cannot be used to determine which of 

the above scenarios is most likely.

5.8.3 The absence of pGSR on a person may be the result of one or more of the 

following;

5.8.3.1 An individual had no association with a firearm.

5.8.3.2 pGSR was not deposited on the individual.

5.8.3.3 pGSR was not retained on the individual.

5.8.3.4 pGSR was not recovered from the surface sampled.

5.8.3.5 pGSR was not detected on the collection device.

References:

(1) ASTM E1588-17, Standard Practice for Gunshot Residue Analysis by Scanning Electron 

Microscopy/Energy Dispersive X-Ray Spectrometry, ASTM International, West 

Conshohocken, PA, 2017, www.astm.org.

(2) Wolten, G. M., Nesbitt, R. S., Calloway, A. R., Loper, G. L., and Jones, P. F., “Final Report 

on Particle Analysis for Gunshot Residue Detection,” Report ATR-77 (7915)-3, Aerospace 

Corporation, Segundo, CA, 1977.

(3) Niewoehner, L., et al., “New Ammunitions for the German Police”. SCANNING - The 

Journal of Scanning Microscopies, Vol. 27, No. 2, 2005, p. 69.

(4) Basu, S., "Formation of Gunshot Residues," Journal of Forensic Sciences, JFSCA, Vol. 27, 

No. 1, Jan. 1982, pp. 72-91.

(5) Zeichner, A., Levin, N., and Springer, E., "Gunshot Residue Particles Formed by Using 

Different Types of Ammunition in the Same Firearm," Journal of Forensic Sciences, JFSCA, 

Vol. 36, No. 4, July 1991, pp. 1020-1026.

(6) Schwoeble, A.J., and Exline, D. Current Methods in Forensic Gunshot Residue Analysis. 

2000.
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(7) Gerard. R. et al. "The Long Range Deposition of GSR and the Mechanism of its 

Transportation." Canadian Society of Forensic Science Journal, Vol. 44, No. 3, 2011, pp 97-

104.

(8) Basu, S., "Fundamental Studies of Gunshot Residue Deposition by Glue-Lift," Journal of 

Forensic Sciences, JFSCA, Vol. 42, No. 4, 1997, pp. 571-581.

(9) Kilty, J. W., “Activity after Shooting and Its Effect on the Retention of Primer Residue,” 

Journal of Forensic Sciences, Vol. 20, No. 2, April 1975, pp. 219-230.

(10) Berk, R.E., "Automated SEM/EDS Analysis of Airbag Residue. II: Airbag Residue as a 

Source of Percussion Primer Residue Particles," Journal of Forensic Sciences, Vol. 54, No. 1, 

2009, pp. 69-76.

(11) Wright DM, Trimpe MA, Summary of the FBI Laboratory’s Gunshot Residue Symposium. 

May 31-June3, 2005. Forensic Science Communication. 2006; 8 (3).