What is Gun Shot Residue (GSR)?

Gunshot Residue, commonly abbreviated as GSR, is the particulate expelled from a firearm during discharge. Linking a suspect to a crime through GSR has been popularized in countless movies and TV shows, but what exactly is GSR?

Scientists began characterizing the particulate from firearms as far back as the 1930s, but it wasn't until the 1970s and the introduction of Scanning Electron Microscope Energy Dispersive X-ray Spectroscopy (SEM-EDS) technology that GSR collection and analysis became so valuable in investigating criminal cases. These powerful tools gave scientists the ability to visualize the microscopic particles and identify the chemical compounds and physical characteristics that identify them as gunshot residue.

The Chemistry of GSR

Contrary to popular belief, the gunshot residue analyzed by RJ Lee Group is not the gunpowder that is used to propel a bullet. The actual source is the primer cap of the cartridge. When a firearm is discharged, the firing pin strikes the primer cap, which causes the primer to burn. This ultimately ignites the gunpowder, causing a buildup of heat and pressure that forces the bullet out of the barrel. 

The primer of a cartridge is comprised of three compounds:

• Lead Styphnate: The primary explosive used in primers because it is sensitive to impact and friction, making it an ideal material to initiate the primer ignition process when struck by the firing pin.
  
  
• Barium Nitrate: Used as an oxidizer to provide the oxygen needed for the combustion of the primer mixture when the firing pin strikes the primer cap.
  
  
• Antimony Sulfide: Acts as a fuel in the primer compound to react with the oxidizer to produce the heat and gas needed to ignite the gunpowder inside the cartridge.

When a firearm is discharged, the lead, barium, and antimony from the primer are vaporized and expelled from the firearm in the form of a gaseous cloud known as a plume. As the plume cools down the elements within it solidify, resulting in the formation of particles that settle on surfaces surrounding the discharge, including hands, clothes, and other surfaces. These particles can then be collected using adhesive stubs.

GSR Particle Types

The GSR particles that deposit on the surfaces surrounding the discharge of a firearm can be classified into three categories.

1. Particles Characteristic of GSR (Three-Component Particles): When lead, antimony and barium combine or condense into a single particle, it is defined as being characteristic of GSR. These particles are the most conclusive evidence of GSR and are typically used to confirm the presence of gunshot residue.
   
   
2. Particles Consistent with GSR (Two-Component Particles): Any particle with two of the three primer metals (lead and barium, lead and antimony, or barium and antimony) is classified as a two-component particle. These particles can come from the discharge of a firearm, but also have some non-firearms sources. Their presence alone is inconclusive to the presence of GSR, but when found with characteristic particles, they can act as part of a GSR population.
   
   
3. Particles Commonly Associated with GSR (One-Component Particles): Any particle with just one of the primer metals (lead, barium or antimony) is classified as a one-component particle. These particles can come from GSR, but have a number of environmental sources. These particles have little weight in GSR examinations.

RJ Lee Group’s GSR Testing

When it comes to analyzing GSR samples, working with the right laboratory partner is crucial for ensuring accurate and reliable results. Because GSR particles are just a few micrometers in size, GSR tests require precise detection and identification. An experienced lab brings years of expertise in handling such delicate and complex analyses, ensuring that every sample is meticulously processed to maintain its integrity.

Our clients choose RJ Lee Group because our expertise and technology ensure that their GSR analysis is accurate and capable of withstanding the rigorous demands of forensic investigation and courtroom scrutiny. Our experts can take the complicated methodology of GSR testing through Scanning Electron Microscopy Energy Dispersive Spectroscopy (SEM-EDS) and easily explain it to law enforcement, attorneys, and jurors. RJ Lee Group’s GSR experts are well-established throughout the United States and beyond as leaders in GSR analysis.