Striated Action Marks

Striated 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.  Some of the more common striated action marks include chamber marks; shear marks, firing pin drag marks, extractor marks, and ejector marks.

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.


Shear Marks

Another common striated action mark are shear marks produced by GLOCK pistols on cartridge case primers.  GLOCK pistols have a rectangular firing pin hole (below) in their breech face.

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.  The resulting striated marks can be seen in the comparison image below.


Firing Pin Drag Marks

In a similar process, striated marks called firing pin drag marks can be produced.  When the firing pin springs forward to strike the primer of a cartridge, it may remain slightly forward and imbedded in the primer.  Certain barrels (like in the GLOCK) drop down slightly as recoil is forcing the action open.  The cartridge case drops with the barrel causing the nose of the protruding firing pin to drag across the primer as it leaves the firing pin impression.  The below comparison image shows firing pin drag marks produced by a Colt 45 AUTO pistol.


Extractor Marks

Another action mark, usually found in a striated form, are those created by the extractor of most auto-loading or repeating firearms.  The extractor is a small part sometimes resembling a hook that is used to remove a cartridge or cartridge case from the chamber of a firearm.  The image below shows the extractor of a 9mm GLOCK pistol hooked into the extractor groove of a cartridge.  As the slide of the pistol moves to the rear, the extractor pulls the cartridge case along with it until it is ejected from the pistol.

The extractor may or may not leave an identifiable mark on the cartridge case.  This is true if the cartridge is fired or simply hand chambered and extracted without firing.  Extractor marks may look like those seen in the comparison image below.  


Ejector Marks

As described above, the extractor pulls the cartridge case out of the firearm's chamber.  As the cartridge case is pulled to the rear it will be struck somewhere on an opposing edge by a part as seen below called the ejector.

The ejector is designed to expel the cartridge case from the action of the firearm.  The resulting impact of the cartridge case with the ejector will cause another action mark that can be used as a means of identification.

Ejector marks can be striated in nature but a lot of the time they are impressed action marks.  Click the next button below to learn more about impressed action marks.

Additional examples of cartridge case comparisons can be seen in the image galleries.

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