Final answer:
There are four types of marks made on a cartridge as a gun is fired: firing pin impression, breech face marks, extractor and ejector marks, and chamber marks. These marks are unique and can be used to link a cartridge to a specific firearm for forensic analysis.
Step-by-step explanation:
When a gun is fired, several marks are made on the cartridge as part of the firing process. These markings are unique to the gun that fired the cartridge and can be used for forensic analysis in criminal investigations. Here are the four main types of marks:
- Firing pin impression: As the trigger is pulled, the firing pin hits the primer of the cartridge, leaving an impression that can vary in shape and size depending on the firearm.
- Breech face marks: When the cartridge is fired, the base of the cartridge case is pushed back against the breech face of the firearm, which is the surface that supports the cartridge at rest. This interaction leaves distinctive scratches or marks on the cartridge case.
- Extractor and ejector marks: The extractor and ejector mechanisms are responsible for removing the spent cartridge from the firearm. The extractor, usually a hook or claw, grips the rim of the cartridge case to pull it rearward, and the ejector forces it out of the firearm. Both components can leave specific marks on the cartridge.
- Chamber marks: As the cartridge is seated in the firearm's chamber, it may acquire unique marks from the chamber's surface due to friction and pressure.
Understanding these marks is important for forensic ballistic experts as they can help link a specific cartridge to the firearm that discharged it. Law enforcement agencies often use this technique as part of their investigation to match bullets and casings found at crime scenes to particular weapons.