Forensic Firearms Examination
Polygonal rifling prevents the forensic firearms examiner from microscopically measuring the width of land and groove impressions because the lands and grooves have a rounded profile instead of a well-defined rectangular profile. In the FBI GRC file, the land and groove widths for these firearms are listed as 0.000. However, it must be noted that forensic identification of firearms is based on microscopic examination of tooling marks on the surface of the bore, produced by the manufacturing-process and modified by the drag of bullet-jackets on that same surface. Thus the bore-surface of individual firearms is always unique.
Read more about this topic: Polygonal Rifling
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