CNN Forensic Files July 19, 2015 07:25:00
The breech face in any gun has unique and distinctive marks from the manufacturing process. >> its subjected to several milling and finishing processes, which cause small, microscopic imperfections to be imparted to the surface. >> and those same marks are imprinted on each and every shell casing that exits that gun. ballistics experts at the pennsylvania state police crime lab were asked to analyze both shell casings. >> when he first got the casing, he said, you know, this is somewhat corroded...
Source: archive.org