What marks are made in a shell casing by the ejector/extractor when the cartridge is expelled from a firearm?

The correct answer, "Extractor impression," refers to the distinct markings left on a shell casing when it is extracted from the chamber of a firearm. The extractor is a component of the firearm that grips the rim of the cartridge case and pulls it out of the chamber after firing. As this happens, the sharp edges or features of the extractor can leave a specific impression or mark on the case, which is characteristic of that particular firearm.

These extractor impressions can be critical for forensic ballistic analysis, as they can help investigators link a shell casing to a specific firearm. Different firearms have unique extractor designs, leading to unique marks, which can be invaluable in criminal investigations.

The other marks mentioned, such as the firing pin impression, refer to the indentation left on the primer of the cartridge by the firing pin when the firearm is discharged. The breech face mark comes from the rear of the chamber, where the cartridge sits, and is pressed against the casing when fired. The rim impression is related to the rim of the cartridge case being affected but does not specifically pertain to the extractor's action when removing the cartridge. Understanding these distinctions is key in forensic science and legal investigations related to firearms.