Comparing Characteristic Markings of Metal Injection Molding and Progressive Die Stamping Extractors
thesisposted on 01.05.2020, 00:00 by Deanna-Kaye D Daley
Introduction: Because it is impossible for two separate machined surfaces to be microscopically identical, a problem can occur if firearm and toolmark examiners are unable to base an identification of weapons and other related components derived from a crime scene. The presence of small parts used in firearms usually produces marks useful in the identification of cartridge cases or bullets that was recently discharged from a firearm. There have been doubts regarding the uniqueness of these and other marks left on the fired evidence obtained due to a lack of characteristic markings (Bonfanti and De Kinder 3-10). Reproducing marks are more liable to happen due to the weapon’s manufacture process. As such, manufacturing processes needs to be investigated as reproducing marks can vary from time to time. Method: After obtaining and prepping the Metal Injection Molded extractors and ammunition as well as the Progressive Die Stamped extractors and ammunition, ten rounds per extractor were fired from a Remington Shotgun and Hi-Point Firearm, respectively. Comparisons for the identification of extractor markings were conducted on the ammunition. Results: Analysis of the Metal Injection Molded extractors concluded that all the Metal Injection Molded extractors were created after being injected in the same mold cavity. After injection of the feedstock into the mold, the produced part was either removed or broken off the mold. This would help to explain why there was no sign of reproducing areas on the inside working surfaces of the extractors due to a grinding or polishing finishing procedure. Reproducing markings were, however, displayed on other areas of the extractor. The markings produced by these extractors were less profound and was determined that this was due to the cartridge contacting the extractor with enough force, but not with as much force as with the Progressive Die Stamped extractor. Further investigation of the Progressive Die Stamped extractors revealed markings identified as markings obtained at the conclusion of the manufacturing process. Additional markings were also seen and was identified as those derived from a sandpaper. The comparison of extractor markings seen within the Progressive Die Stamped extractors revealed significant agreement of the overall pattern among each group of extractors. The markings produced by these extractors were more profound and it was determined that this was due to the cartridge contacting the extractor with much force. When comparing markings from various extractor groups, it was found that more differences than similarities existed among the markings. Although there were more similarities among the Metal Injection Molded markings produced by different extractors when conducting an inner comparison, these markings can statistically and microscopically be differentiated. Conclusion: Although microscopic comparisons produced similarities among the extractor markings from both manufacturing processes, mass produced parts by modern manufacturing processes; Metal Injection Molding and Progressive Die Stamping, can differentiated by firearm examiners after comparing fired evidence.