AFTE Store - Drywall: Terminal Ballistic Properties of Forensic Interest

Drywall, also known as sheetrock and wallboard, is common in homes and offices as a means of constructing interior walls. The product comes in several popular thicknesses and consists of pressed, semi-hydrous gypsum covered with a heavy paper layer on both surfaces. Popular thicknesses in the United States are 1/2-inch (12.7mm) and 5/8-inch (15.9mm). A much less common thickness of 3/8-inch (9.5mm) is also available. Once nailed onto the supporting structures, the nails and joints are usually covered and the exposed surface painted or covered with wallpaper. Drywall is often struck and perforated by bullets discharged in shootings that occur indoors. The velocity necessary for medium caliber pistol bullets to perforate common drywall is relatively low- on the order of 100 to 170f/s (30-52m/s) depending on the weight of the bullet and its orientation at the moment of impact. The velocity loss experienced by such bullets during the penetration and perforation process is also quite low and on the order of 40 to 50f/s (12-15m/s) for common +-inch thick drywall. Bullet deflection as a consequence of perforation is virtually non-existent making the reconstruction of a bullet’s preimpact flight path from the entry hole and a subsequent downrange impact point very reliable. The ejection of displaced calcium sulfate from the exit side of a panel of drywall takes place along a path that is orthogonal to the bullet’s exit site and not necessarily according to the flight path of the bullet. This dislodged material may be found adhering to a nearby opposing surface within the struck wall and can lead to serious errors in reconstructing the flight path of a shot into such a wall if it is used for that purpose.