The lead-in method for bullet impacts in metal panels

Abstract

The use of trajectory rods at shooting scenes to document a bullet’s trajectory is useful since the probing method provides for an immediate visual reference as to where the projectile came from and where it may have been traveling to. Trajectory rods are also quite simple to measure with manual tools. However, the use of trajectory rods is not always possible because a bullet may strike a relatively thin material, such as a metal panel, creating a bullet impact that is not suitable for determining the bullet’s path using the probing method. In these cases, it may be possible to use the elliptical method or the lead-in method. The ellipse method has been shown to have some of its own challenges when the bullet impact site is highly deformed while the lead-in method is less studied and only useful over lower ranges of impact angles. This study looks to define the lead-in method and then test its performance with 15 blind participants and 5 different calibers, each with two different types of ammunition. The results of this study have shown that each combination of caliber and ammunition has its own characteristic error curve that appears to change with the known impact angle. Errors do not remain constant and in some cases, the errors exceed 20°. The range of errors is greater at higher angles of incidence where the lead-in area is relatively small. The procedures outlined in this study propose a method of use, highlight limitations, and provide insight into the accuracy for the lead-in method.