AFTE Store - The Trig-Elliptical Method of Bullet Impact Angle Determination

This paper describes a new method for determining the horizontal impact angle (or bearing) of single bullet holes using the trigonometric theory. This method uses digital imaging and a commonly available computer tool to better define the elliptical properties of bullet holes resulting in more precise measurements and more accurate angle determinations. As a result of tests conducted in 2 inch drywall, this method was determined to be useful for bullet holes resulting from shots fired at horizontal angles of between 5 and 60 degrees, with error rates no greater than +/- 4 to +/- 6 degrees. The useful range of this method accounts for approximately 2/3 of all possible impact angles. Benefits of this method are: 1) increased accuracy, 2) more bullet holes suitable for angle determination, and 3) it works from images/photographs so that, as long as good crime scene documentation exists, angle determination and trajectory analysis may be performed on old crime scenes, even after the bullet holes are no longer present.