page_title: Forensic firearm examination
section_title: Examination of cartridges
hierarchical_section_title: Forensic firearm examination / Examination of cartridges
caption_attribution_description: English: ID Dynamics / Todd Lizotte Reference Images / Ballistic Microstamping
context_page_description: Forensic firearm examination is the forensic process of examining the characteristics of firearms or bullets left behind at a crime scene. Specialists in this field are tasked with linking bullets to weapons and weapons to individuals. Obliterated serial numbers can be raised and recorded in an attempt to find the registered owner of the weapon. Nitric acid is the most common reagent used for this. Examiners can also look for fingerprints on the weapon and cartridges. Fingerprints are key pieces of evidence. If crime scene investigators find prints at a scene, they will be dusted, photographed, collected, and analyzed both by hand as well as compared to databases for potential references.
  By examining unique striations, scratches left behind on the bullet and weapon, individual fired rounds can be, but not always are, linked back to a specific weapon. These striations are due to the rifling inside the barrel of handguns. Rifling spins the bullet when it is shot out of the barrel to improve accuracy.
context_section_description: Spent cartridges found at a scene can be examined for physical evidence such as fingerprints or compared to samples that match them to a weapon. The examination of the cartridge relies on the unique tool marks left by the various parts of the weapon including the firing pin and the ejector in semi and fully automatic firearms. These markings can be compared and matched to known exemplars fired from the same weapon using the same parts. The examination of the marks left on the cartridge is done using a comparison microscope. Examiners view the questioned cartridge and the known exemplar simultaneously, looking for similar microscopic marks left during the firing process.
  Cartridges are also routinely examined for fingerprints as the act of loading the ammunition into the magazine, or chamber, leaves recoverable impressions.  These fingerprints can survive the firing processes and, while a rare occurrence, fingerprints have been obtained from cartridges recovered from the scene. Cartridges are subjected to cyanoacrylate fuming and examined for any usable prints. Usable prints are photographed and can be uploaded to fingerprint databases such as IAFIS for comparison with known exemplars. Cartridges can also be swabbed for trace DNA left by the individual who loaded the magazine. The extremely low levels of recoverable DNA present the same issues as swabbing a firearm for DNA.
  Advancements in microscopic stamping have led to a push for the inclusion of firing pin microstamping. The microstamp is etched onto the firing pin and is transferred to the cartridge during the firing process. Each firing pin would have a unique serial number allowing investigators to trace casings found at a crime scene to a known firearm. The practice is not in use as of 2020, although California has enacted legislation that requires microstamping on all newly sold firearms. The law, and microstamping in general, has received significant opposition from gun manufacturers due to increased costs associated with introducing the microstamps into the manufacturing lines.
caption: Example of microstamping. Insert shows a close up of the serial number imprinted into the cartridge.
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