"Test Four - Wallboard - Two pieces of ½ inch standard gypsum board are set 3.5 inches apart. The gelatin block is placed 18 inches behind the rear most piece of gypsum. This test event simulates a typical interior building wall." This test evaluates the performance of a small arm bullet fired at a subject using the wall of an interior room as protective cover. While an 'easy' medium to penetrate, wall board is insidious to rifle bullets and hollowpoint pistol bullets - it tends to turn a rifle bullet on its side (greatly decreasing penetration and increasing the risk of bullet fragmentation) and tends to plug up the cavity of hollowpoint handgun bullets - causing a failure to fully expand or to expand at all. In this case, the risk of overpenetration with a shotgun used defensively inside a structure (in the event of a complete miss of the intended target) was assessed. All standards were met with the test setup, the block was also faced with two layers of 12 oz. denim fabric to simulate light clothing. Firearm was 20" barrel, cylinder choked pump shotgun. Ammunition was 12 gauge Winchester 3" magnum #1 unplated buckshot. Block calibrated at 9.2cm and '541 ft/sec' impact velocity (chronograph malfunction). Average penetration was 11.8", with the shallowest pellet going 9.0" and the deepest penetration occuring at 14.4". Pellets were only moderately deformed, average diameter ~ 0.30". Impact velocity was not recorded due to chronograph malfunction during the calibration shot. Apparently, the lighting level at the test area was changing rapidly due to fast moving rain clouds above the test area.