Tag Archives: firearm

FBI Gun Collection

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Gun collection

FBI Gun Collection. Source: FBI.

 

Earlier this month, the FBI posted a story about the agency’s reference firearms collection. Started in 1933, the collection of 7,000 firearms is stored at the FBI Laboratory in Quantico, Virginia.

FBI Lab firearms examiners use the assembly of weapons to study and test firearms in support of current investigations. The library of handguns and rifles includes a database of typical marks made by the weapons, and more than 15,000 types of commercial and military ammunition. Suppressors, magazines, muzzle attachments, grenade launchers and rocket launchers also reside here.

“Oftentimes this collection is used in active cases in comparing known samples from our collection with question samples from the field,” explained FBI firearms examiner John Webb. “Often, an investigator will receive a part of a firearm or a firearm that isn’t functional. We can take that and compare it with our reference collection, determine what isn’t functioning, and repair it so we can obtain the test fires we need to conduct examinations with bullets and cartridge cases.”

 

GSR Speaks Again

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Traditionally, gunshot residue contained gunpowder residues (such as partially-burned or unburned gunpowder) and lead residues. However, an increasing number of ammunition manufacturers produce ammunition that contains little or no lead. This change is good for the environment, but creates a challenge for criminal investigators, because crime labs test for gunshot residue by detecting the presence of lead, barium, and antimony.

During June 2012, forensic researchers at Florida International University announced a new technique that can potentially link a suspect to fired ammunition by identifying the chemical signature of the powder inside a bullet. In this approach, a chemist analyzes the chemical composition of a bullet’s smokeless powder. The method reveals the particular formula of the smokeless powder, which further identifies the manufacturer of the powder.

“Crime labs all over the country are faced with the reality that their only way to analyze whether a gun was fired by a suspect may become obsolete,” said chemistry Professor Bruce McCord in a press release. “Our discovery is not only more accurate, but it can determine the type of gunpowder used in a crime even if the gun is never recovered.”

GSR Speaks

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Gas precedes a fired bullet.

When a bullet leaves the muzzle, it is preceded by a gas bubble. Source: Alexander Jason, “Effect of Hair on the Deposition of Gunshot Residue,” Forensic Science Communications 6(2) (April 2004).

In a shooting, gunshot residue (GSR) can be found on the victim, on surfaces within a few feet of the sides of the firearm, and on the hands of the shooter. The excellent FirearmsId.com website offers a brief description of GSR generation:

When the firing pin of a firearm strikes the primer of a cartridge the primer compound ignites sending a flame into the cartridge case. Gunpowder in the cartridge case starts to burn, causing it to change from a solid material to a gas. This change creates pressure within the cartridge, which in turn forces the bullet down the barrel and down range. Pressure building behind the bullet is released when the bullet exits the muzzle of the firearm.

The bullet acts like the cork in a shook up Champagne bottle. When the bullet exits the muzzle, pressure behind it blows the gunshot residues out of the firearm’s barrel under high velocity. The residues are expelled from the barrel in a smoky cone shaped pattern.

Analysis of GSR can establish that a shooting took place and may link a person with that shooting. One day, GSR may reveal more details about a shooting. On June 18, 2012, University at Albany (New York) researchers announced that they developed a method to determine the caliber and type of weapon used in a crime by analyzing GSR. The technique uses spectroscopy with laser light. Lead researcher Igor Lednev cautioned that his team must continue their research before the method can be presented in a courtroom.