Obturatormerkkejä

Obturatormerkkejä is a Finnish term that translates to "shutter marks" or "obturation marks" in English. These marks are typically observed in firearms and refer to impressions left on the base of a cartridge case. These impressions are caused by the breech face of the firearm coming into contact with the cartridge case during the firing process, specifically when the bolt or breechblock closes.

The primary purpose of the breech face is to seal the rear of the cartridge chamber, preventing hot gases from escaping backward. When the firearm is discharged, the expanding gases push the cartridge case rearward against the breech face. This forceful contact can imprint the microscopic texture and imperfections of the breech face onto the softer metal of the cartridge case base. These imprints are unique to the firearm that fired the cartridge.

Forensic ballistics often utilizes obturatement marks as a form of firearm identification. By comparing the obturatement marks on a fired cartridge case found at a crime scene with those from a test-fired suspected weapon, investigators can determine if that specific weapon was used. The pattern of striations, scratches, and other irregularities on the breech face are transferred to the case, creating a unique signature. Analyzing these marks under a microscope allows for a detailed comparison.

The presence and clarity of obturatement marks can vary depending on factors such as the firearm's condition, the ammunition used, and the force of ejection. However, they are considered a valuable tool in the field of forensic science for linking ammunition to a particular firearm.