AFTE Store - Improving the Comparison Value of M-16’s Barrel Extension Lug Marks

Barrel extension lug marks on 5.56X45 mm cartridge cases have been known to the forensic firearm examiners community for a number of years [1]. These marks occur during the extraction and ejection cycle of the M-16. As the extractor draws the cartridge case out of the chamber, the spring loaded ejector forces the cartridge case toward two specific barrel extension lugs. This report will refer specifically to their appearance, repeatability and quality. The test fire results and application of statistical inference led us to realize that these marks can be directly influenced by the shooting mode (full automatic vs semi-automatic). In some of the cases, it will be possible to ascertain the shooting mode when the M-16 assault rifle is missing.