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more substantial indents on the cartridge head near the rim. Analysis of ejector marks can be made more difficult by the fact that the rim of the cartridge head is also where ammunition makers put their headstamp (brand identifier) and information on the size and caliber of the cartridge. These heavy-set alphanumeric characters are inscribed on the cartridge brass and—depending on where the ejector happens to hit—parts of the stamp may bleed into the ejector mark.
In addition to the shape of the ejector mark and any individual scrapes or textures therein, ejector marks also serve the same important purpose as a firing pin drag mark: They provide a point of reference for proper orientation of cartridge cases relative to each other in comparison.
During the firing process, gas pressure works on all surfaces, forcing the material of the cartridge against the chamber of the weapon; particularly in semiautomatic weapons, other firearms parts are used to circulate ammunition through the weapon and eject spent casings. These actions and parts can lead to a host of marks on the cartridge case that—though not imaged using current techniques—are sometimes used by examiners studying matches between pieces of evidence.
Chamber marks are parallel striated marks along the outer walls of the cartridge case, impressions from the scraping used to bore or ream the chamber (along with the rest of the barrel) from a solid piece of alloy. The extractor in a pistol that helps move a spent cartridge out of the chamber is typically a small arm that fits over the rim of the casing, holding it as the breech assembly slides backward. Accordingly, the extractor can leave marks where it makes contact, either on the edge of the rim of the cartridge head or on the neck separating the head from the main body. The slide that moves back and forth in semiautomatic pistols, allowing ejected casings to move away from the weapon, may leave a scuff mark on the edge of the cartridge head and a rough drag mark along the cartridge wall. As individual cartridges move from a magazine into chamber, a mark on the outer wall of the case may be caused by the magazine lip.
2–C.2 Bullet Markings
Hatcher’s (1935:255) seminal text on firearms identification referred to “the fine ridges and grooves on the surface of the bullet, parallel to the rifling marks,” as “the most important individual characteristics which are used” in the field. These marks on the bullet—known as striations or striae—“are caused by its passage over surface irregularities and rough spots on the interior of the gun barrel that got there principally during