Firearms analysis

DEFINITION: Examination of bullets, cartridge cases, and firearms marks as well as identification and functionality testing of firearms.

SIGNIFICANCE: Firearms may be used in crimes in a wide variety of ways, and law-enforcement investigations involving firearms must examine a wide range of forensic evidence. Because the use of firearms varies so much from crime to crime, methods of firearms analysis also vary, with investigators and forensic experts relying on a mixture of chemistry, physics, and technology to conduct their examinations.

The field of forensic firearms analysis has grown from the traditional study of to include detailed analysis relying on the fields of chemistry, physics, engineering, mathematics, and other traditional disciplines. The very nature of modern firearms, along with the varied ways in which firearms are used in criminal activities, means that firearms analysis requires a high level of expertise.

Early firearms analysis focused primarily on the identification of bullets, cartridge cases, and firearms marks. One of the more famous cases that relied on bullet identification took place during the US Civil War, after Confederate general Stonewall Jackson was shot returning to his camp after a battle. The wound resulted in Jackson’s death a little more than a week later. Experts were called to examine the recovered projectile and, after careful analysis, determined that the bullet—based on its size and shape—was not the same as the type used by the Union Army. This likely meant that Jackson was shot not by an enemy soldier but instead by one of his own troops.

Ballistics and Firearms Identification

The term “ballistics” refers to the study of the motion, behavior, and effects of projectiles. This includes bullets, aerial bombs, rockets, and other projectiles. Most commonly, the term is applied to the science and art of accurately sending a projectile through the air to achieve a desired performance. As used by forensic analysts, “ballistics” refers to the study of projectiles to determine their origin as well as their use and implementation.

Firearms identification is closely associated with ballistics, as both focus on the nature of the projectile, as well as the method for sending it through the air. The major categories in firearms identification include types of firearms, manufacturing techniques, design, construction, and function. A common task for law-enforcement investigators following a criminal act involving a firearm is the recovery of the projectiles fired, with the aim of matching them to the firearm that fired them.

Firearms Types and Ammunition

The type of firearm and the specific ammunition chosen for a criminal act are often important factors in the investigation. Certain firearms, such as pistols, can be easily concealed and are used when stealth or convenience is required. Rifles and shotguns present very different usage parameters and so are typically related to specific types of crimes. The identification of the types of firearms used is important in the investigation of crimes such as and murder.

“Ammunition” generally refers to the method and type of projectile in question. Modern firearms rely on a cartridge system, which brings bullet, gunpowder, and sparking mechanism together into a single unit that can be easily loaded for quick use. Firearms analysis focuses on the individual components as well as their use. Experts in bullet and cartridge case identification focus on size, shape, weight, and manufacturer marks to help identify related to crime involving firearms.

Collection and Analysis of Firearms Evidence

Crime scene technicians are responsible for the location and recovery of projectiles used in firearms-related cases. The methods for recovering both fired bullets and spent cartridges vary depending on the nature of the crime and conditions. The focus in recovering a fired bullet is often on recovering the evidence in a manner that will least affect its condition.

Forensic analysts traditionally work in laboratories or other secured facilities when examining firearms, bullets, cartridges, and other firearms-related evidence. A common task is the comparison of bullets or firearm parts to determine the likelihood of match with a firearm. Modern pistols and rifles have grooves cut inside their barrels to help control the accuracy of fired projectiles. This means that for many modern firearms, the interaction of a fired bullet with the barrel of the gun often leaves distinct markings that can be used to match the bullet with the gun.

Another matching technique uses the impression left on the cartridge from the firing pin or other parts. The firing pin strikes the end of the cartridge, causing a chemically ignited spark that ignites the gunpowder. A great deal of force is necessary to cause the firing pin to strike the cartridge, which in turn ignites the gunpowder. This force leaves an impression of the firing pin on the cartridge that can be matched in many instances.

The matching of a bullet with barrel grooves and the matching of a firing pin to the impression on a cartridge rely on similar techniques. Known commonly as impression comparison, these techniques focus on similarities between the bullet or cartridge in question and the potential source of the impression.

Firearms analysis has advanced to the point that detailed databases exist to help forensic scientists in impression comparison and identification. Both firearms and ammunition manufacturers and investigative agencies maintain such databases, often in cooperation with one another. Such databases are especially useful in the establishment of baseline identification methods. Because of advanced firearms analysis, law enforcement in March 2022 were able to link the shootings of five homeless men in Manhattan and Washington, DC, to the same gun and arrested the shooter.

Trajectory and Other Firearms Analysis

The term “trajectory” commonly refers to the path a bullet or other projectile takes in flight or after contact with an object. Both forces of nature (such as wind) and manufacturing characteristics can affect the way a bullet is propelled through the air. Analysis of a bullet’s may help establish where the shooter was in relation to the victim, as well as the degree and type of injury sustained.

In complex cases involving firearms, especially those in which multiple shots were fired or multiple shooters were involved, forensic scientists determine the angles and paths of the bullets through trajectory analysis. This method of analysis relies heavily on known characteristics of guns and ammunition, as well as on the science of physics.

Firearms analysis may also involve questions of injury and nature of use. The type of bullet as well as the type of firearm can affect dramatically the type of injury to the victim and the damage to any property or physical item struck by the bullet. The analysis of such injury or damage can help determine the relationship between shooter and victim, as well as answer potential questions of conduct during the shooting. For example, the presence of gunpowder residue on a victim’s skin generally indicates that the weapon was close to the victim at the time it was fired; this information may support or disprove statements regarding the events that took place.

In 2023, experts from the National Institute of Justice (NIJ) reported having studied gunshot acoustics for about eight years. They wanted to see if it was possible to identify a gunshot by listening to a high-quality recording. Audio evidence could come from a variety of sources, including smartphones, body cameras, and surveillance systems. In addition to helping experts identify a type of gun, audio forensic analysis may reveal details such as the shooter's location and orientation.

Bibliography

"The Emerging Field of Firearms Audio Forensics." National Institute of Justice (NIJ), 7 Aug. 2023, nij.ojp.gov/topics/articles/emerging-field-firearms-audio-forensics. Accessed 15 Aug. 2024.

Heard, Brian J. Handbook of Firearms and Ballistics: Examining and Interpreting Forensic Evidence. New York: John Wiley & Sons, 1997.

Hueske, Edward E. Practical Analysis and Reconstruction of Shooting Incidents. Boca Raton, Fla.: CRC Press, 2006.

Schwoeble, A. J., and David L. Exline. Current Methods in Forensic Gunshot Residue Analysis. Boca Raton, Fla.: CRC Press, 2000.

Sharma, B. R. Firearms in Criminal Investigations and Trials. New York: Universal Law Publishing, 2004.

Valerio, Raymond and Nelson Bunn. "Firearm Forensics Has Proven Reliable in the Courtroom. And in the Lab. Scientific American, 27 Nov. 2023, www.scientificamerican.com/article/firearm-forensics-has-proven-reliable-in-the-courtroom-and-in-the-lab/. Accessed 15 Aug. 2024.