Ballistic fingerprints
Ballistic fingerprints refer to the unique marks left on bullets as they are fired through the barrel of a firearm, specifically the striations created by the rifling inside the barrel. This process is part of internal ballistics, which examines the events from the moment a bullet is propelled until it exits the firearm. Ballistic fingerprinting plays a crucial role in criminal investigations, as forensic experts analyze these markings to match bullets to specific firearms, aiding in solving crimes. The concept dates back to the early 20th century, with significant advancements over the years, including the development of digitized databases that allow law enforcement to compare ballistic fingerprints from crime scenes.
While ballistic fingerprinting is effective for identifying firearms in many cases, it is not applicable to shotgun pellets due to their smooth bores. The process can be labor-intensive, often requiring hours of microscopic comparison. Additionally, microstamping technology has emerged as a proactive measure, imprinting firearms with unique codes to aid in tracing bullets back to their source. Some U.S. states have enacted laws mandating microstamping for new handguns, though the effectiveness and objectivity of ballistic fingerprinting remain topics of ongoing debate within the legal and forensic communities.
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Ballistic fingerprints
DEFINITION: Marks that are etched on a rifle or handgun bullet as it is pushed through the gun’s barrel.
SIGNIFICANCE: The analysis of ballistic fingerprints is used in criminal investigations to gain information about the models of guns as well as the individual guns that fired bullets recovered from crime scenes. By comparing the marks that guns leave on bullets, experts can often identify the weapons used in crimes.
The examination of ballistic fingerprints is part of the field of internal ballistics, which is the study of events that begin when the firing pin of a rifle or handgun strikes the cartridge and end when the bullet exits the barrel. It is most commonly associated with ballistics in crime scene investigation. Ballistic fingerprinting is not a new science. In June, 1900, Dr. Albert Llewellyn Hall published an article titled “The Missile and the Weapon” in the Buffalo Medical Journal, in which he presented the first analysis of bullet marks imparted by rifling in a gun barrel.
The interior of the barrel of a rifle or handgun has raised and lowered spirals, called rifling, that impart spin to the bullets as they are fired, making them more aerodynamically stable. As a bullet is pushed down a gun’s barrel by the gas that is generated by burning gunpowder, it is etched with fine lines, or striations, from the rifling. Under microscopic examination, these striations look something like the parallel lines of a universal product code. In addition, “skid marks” may be left on a bullet in the short period after it leaves the firing chamber and before it is fully engaged by the rifling.
The striations common to all guns of a particular model are known as class characteristics. Individual characteristics are the striations unique to a particular gun; these result from tiny imperfections in the rifling process and in the rifling tools used as well as from the wear and tear caused by the particular usage of that gun. Individual characteristics change over time. Criminals sometimes deliberately change a gun’s individual characteristics; common techniques include shortening the barrel and rubbing the interior of the barrel with a steel brush.
Different types of ammunition fired through the same gun will produce very different striations. Even the small natural variations from one cartridge to another in the same box of commercial ammunition can produce some differences in patterns.
The analysis of ballistic fingerprints produces its most accurate results when the cartridge case (which holds the bullet, gunpowder, and primer before firing) as well as the bullet has been recovered; the firing pin, extractor, magazine, and other parts of the gun often leave distinctive marks on the case. Ballistic fingerprinting cannot be used on shotgun pellets because shotgun bores are smooth rather than rifled. However, shotgun cases can still be examined for firing pin marks and the like.
Several databases of digitized ballistic fingerprints of bullets recovered from crime scenes are available to criminal investigators, including state databases in Maryland and Connecticut. Forensic experts who conduct ballistic fingerprinting can use these databases to narrow their selection of bullets for microscopic examination. Binocular microscopic comparison of two bullets can take many hours.
A few jurisdictions require that ballistic fingerprint samples from new, lawfully sold handguns be put into a digitized database, but the efficacy of such efforts is the source of ongoing debate along with other gun laws. One controversial subject is the introduction of microstamping, a process in which guns are produced with microscopic markings specially designed to imprint a code on each bullet that records the specific gun's serial number, make, and model. Proponents of the system claim that it is more effective for correctly identifying guns used in crimes. In 2007, California became the first state to require microstamping in new handguns, and the District of Columbia had enacted similar legislation that became effective in 2016. In 2022, New York also passed legislation requiring microstamping in new handguns. New Jersey did not require microstamping, but it offered rebates and incentives to entice gun manufacturers to use microstamping. However, some experts viewed identifying ballistic fingerprints as subjective, causing some courts to reconsider whether they should be required.
Bibliography
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