Module 4 - Forensic Ballistics
Lesson 2 - Ballistic Fingerprinting and Wound Ballistics
Cartridge Identification Methods
The microscopic land and groove impressions found on the surface of fired bullets are routinely used to match bullets with a suspects’ weapons. Impressions can be found on cartridge cases as well, and these can be used to match a cartridge case to a specific firearm. Firing pin impressions, extractor marks, ejector marks, chamber marks, and ammunition stamps on the cartridge casing are all features analyzed by forensic firearm experts.
Firing pin impressions are left during the discharge of a firearm. The firing pin creates microscopic features of the indentation left when it strikes the primer of a cartridge.
Extractor and ejector marks are produced when the cartridge case is mechanically extracted from the chamber. Visible fine striations and impressions are left on the rim and head of the casing.
Chamber marks are parallel striations on the cartridge case caused by contact with the walls of the chamber of the firearm.
Ammunition stamps consist of information about the type of ammunition stamped by the manufacturer onto the base of the cartridge casing.
An example of an ammunition stamp.
- Source: FederalPremium.com
Ballistic Databases
Forensic Technology Inc., a Canadian company located in Montreal, Quebec, has developed a computerized ballistic fingerprinting system called Integrated Ballistic Identification System (IBIS). IBIS creates digital images of the markings left on bullets and shell casings. This allows them to be compared easily to a database of images. When the system finds a bullet or cartridge casing that has similar markings, firearms experts compare these markings to the original evidence to determine whether a match has been made. IBIS minimizes the amount of time firearms experts spend viewing non-matching evidence. Consequently, law enforcement agencies are able to discover links between crimes more efficiently.
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The US Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF) utilizes IBIS in coordinating one of the largest ballistic fingerprinting programs in the world. The ATF’s National Integrated Ballistic Information Network (NIBIN) contains detailed ballistic information about firearms that have been seized from crime scenes across the United States. Since ATF began using IBIS, more than 926 000 pieces of crime scene evidence have been entered into the database resulting in more than 12 500 positive identifications (hits). |
| In December 2006, police in Detroit, Michigan, responded to a report of shots being fired. When officers arrived, they learned that a suspect had approached two people in a vehicle and fired several shots at them. Key characteristics associated with several cartridge casings and bullets recovered from the crime scene were entered into NIBIN. A month later, a suspect was arrested for possessing a pistol during an unrelated drug-trafficking investigation. The pistol was submitted for test firing, and subsequent images were entered into IBIS. This resulted in a match to the ballistic evidence recovered at the shooting that had occurred a month earlier. |
Firing Pin Impressions
- The microscopic features of the indentation left when the firing pin strikes the primer of a cartridge, discharging the firearm
Extractor and Ejector Marks
- The marks produced when the cartridge case is mechanically extracted from the chamber. Visible fine striations and impressions are left on the rim and head of the casing.
Chamber Marks
- Parallel Striations on the cartridge case caused by contact with the walls of the chamber of the firearm
Ammunition Stamps
- Information about the type of ammunition stamped by the manufacturer onto the base of the cartridge casing