Experimental estimation of an incidence angle of a fired bullet based on the damage on an automobile windshield

Abstract

  Handgun bullets fired toward the windshield of an automobile sometimes ricochets. In such a case, we must estimate the type of bullet and direction of shooting from the damaged windshield. The purpose of this study is to obtain a method to estimate the fired direction of a handgun bullet from the fractured windshield. We test fired bullets to an automobile windshield with various incidence angles. The thickness of the windshield is slightly different from model to model of the automobiles. In the beginning, we examined the strength of the automobile windshield of various car models. First, we examined the static failure strength of the windshield by an indentation test. In this test, fracture load and the amount of indentation were measured on windshield samples cut from ten models of Japanese automobiles. Next, we test fired a handgun in order to examine the relation between the trajectory of a bullet and the collision marks on the windshield. The cartridges used in these test firings were 38SPL. lead round nose (LRN) bullet and full metal cased (FMC) bullet. In the results of static indentation test for different car models, there was found to be almost no differences in the relationship between fracture load and indentation depth. With the LRN bullet, bullets perforated the windshield when the incidence angle was less than 45 degrees and ricocheted when the incidence angle was greater than 60 degrees. In these cases, a characteristic damage was left on the windshield. On the other hand, FMC bullets of 38SPL. perforated the windshield when the incidence angle was less than 60 degrees and ricocheted when the incidence angle was greater than 70 degrees. Based on these results, we proposed a method to estimate the direction of shooting in criminal cases in which a bullet was fired on an automobile windshield.