Cartridge Case Identification

Like bullets, cartridge cases can be identified as having been fired by a specific firearm.  As soon as cartridges are loaded into a firearm the potential for the transfer of unique tool marks exists.  However, the cartridge does not have to be fired for these marks to be transferred.  Simply loading a cartridge into a firearm can cause unique identifiable marks that can be later identified.

Cartridge cases like those on the right are mostly made of brass but can also be made of other materials such as steel and plastic.  Cartridge cases come in a variety of finishes but all are made of a material that is softer than the materials found in a firearm.  Any surface of the cartridge case that meets the inner workings of the firearm may be marked.

Tool marks produced on the cartridge cases will be in two basic forms.  As the microscopic striations found on bullets, cartridge cases can pick up striated action marks. These "scratches" are produced when the cartridge case moves laterally against the tool (inner surface of the firearm) producing a scrape or striated mark.  The other form of marks that can be left on a cartridge case are impressed action marks.  Impressed marks are created on cartridge cases when it impacts the tool (again, the firearm) with adequate velocity or pressure to leave an impressed or indented mark.

Cartridge cases are compared to fired standards from a firearm using a comparison microscope as described on the bullet identification page.  Standards are first examined to determine what marks, if any, the firearm is consistently reproducing. Evidence cartridge cases are then directly compared to the standards to see if they too are also similarly marked.

Cartridge case comparison results may be reported as follows:

Exhibit 1 (cartridge case) was identified as having been fired by Exhibit 2 (firearm).

The above conclusion is reached if the action marks present on the questioned cartridge case are determined to be because of the actual firing process.  An example of which can be breech marks as seen in the comparison image below.


Exhibit 1 (cartridge case) could neither be identified nor eliminated as having been fired by Exhibit 2 (firearm).

The above conclusion is reached if the cartridge case lacks sufficient action marks to be identified as having been fired by the questioned firearm or the firearm in question fails to produce reproducible individual characteristics on standards.  All general class characteristics such as caliber and firing pin shape would have to agree.  The image below shows a comparison between two cartridge cases that lack any individual characteristics but have a similar general appearance.


Exhibit 1 (cartridge case) was not fired by Exhibit 2 (firearm).

This conclusion can sometimes be reached when the submitted cartridge case exhibits very good individual characteristics that are very dissimilar to those produced on standards.  However, consideration must be given to the possibility that the firearm in question could have changed significantly.  If all dissimilarities can be accounted for, a negative conclusion will be reached.  The comparison image below shows two cartridge cases that exhibit noticeably different breech marks and firing pin impressions.


Exhibit 1 (cartridge case) was identified as having passed through the action of Exhibit 2 (firearm).

This conclusion can be reached if the cartridge case is found to have action marks that result from simply loading and/or unloading a cartridge case in a firearm.  The comparison image below shows striated action marks on the shoulder of cartridges that have been loaded and unloaded in a Chinese AK Type assault rifle.


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