Along with the identification of fired bullets, the identification of fired cartridge cases and shotshell cases comprise two key aspects of firearms examination. Fired cartridge cases are frequently more useful than fired bullets when linking shooting incidents because they are usually found in greater quantities at crime scenes. They may also bear more microscopic marks of value than recovered bullets, which are subject to mutilation, deformation, and fragmentation.
The identification of fired cartridge cases and shotshell cases dates to 1925 when a comparison microscope was modified to compare the unique microscopic marks produced by firearms on the surfaces of ammunition. This was accomplished by the Bureau of Forensic Ballistics, a private group in New York City led by Calvin H. Goddard.