2019
Eric Law
Nashville, TN
This presentation will assist the audience to better understand the variability within the double-casting process through use of an IBIS Heritage System, as well as applications of double-casting in forensic science.
Due to the variability that arises in the breech face and firing pin impressions on multiple cartridge cases fired by the same firearm, a method of reproduction is needed to create standardized cartridge cases. A process called double-casting has been used that involves creating s silicone rubber mold of a cartridge case, and then uses a plastic resin casting material to make a cartridge case reproduction. The first part of this study analyzed casts of the National Institute of Standards and Technology (NIST) standard cartridge case (SRM 2461). Integrated Ballistic Identification System (IBIS) data and visual comparisons showed the method of double-casting was able to reproduce fine detail that is visible even at 100x magnification. Prior to widespread use, it is important to characterize the effects of within-and between-mold variability of the casts.
Twenty-five cartridges were fired by a SCCY CPX-2, Hi-Point C9, and a Smith & Wesson SD9VE and the cartridge cases were replicated using the double-casting process. Three molds were created for each cartridge case, and five sets of double casts were made from each of those molds. In total, 1125 double-casts were entered into an IBIS Heritage System. Which- and between-mold comparisons were performed for each firearm utilizing the breech face and firing pin correlation scores as a measure of similarity between the images. Some instances of significant differences between the mold and cast sets were found. However, visual comparisons of (1) the casts to their original cartridge cases, and (2) the casts to other casts of the same cartridge case both showed that the double-casting method reliably reproduces the fine detail that is present on the original cartridge cases.
Double-casting has many potential applications. The pattern interpretation areas of forensic science are frequently criticized due to their subjective nature, and many of these critiques have been summarized in the NAS and PCAST reports. To strengthen the scientific foundations of firearms examination, the reproducibility of cartridge case comparison need to be known. Reproducibility will ensure that different examiners reach the same conclusion when comparing cartridge cases with the same level of detail. The double-casting method described above is currently being applied for this purpose.