CCID - Striated Action Marks S triated action marks are common to cartridge cases that have passed through the action of an auto loading or repeating firearm. Striated action marks can be produced on cartridge cases by contact with a number of different areas within the firearm. Chamber Marks One of the most common striated action marks are called chamber marks . Roughness in the chamber of a firearm can scratch the outer walls of a cartridge case when loaded and removed from the chamber. Most chamber marks occur after the cartridge is fired.
Cartridge cases expand when fired pressing out against the walls of the chamber.
When they are pulled out of the chamber, the sides of the cartridge case can be scratched. The comparison image below shows chamber marks on 22 caliber, rimfire cartridge cases. When a cartridge case is forced backwards from recoil the primer imbeds itself in the firing pin hole. As the slide of the pistol starts to recoil, the barrel will drop slightly as the action opens. The dropping barrel forces the cartridge case to move down slightly and when this happens the lower edge of the imbedded primer is sheared downward and out of the firing pin hole.