I made some frames with 4 layers of sheetrock separated by 2x4s. Used a Remington 870, 12ga, 20" IC choke, and #8 birdshot, #5 bird, and #4 "tactical" buck. At 7 paces (approx 18 feet), the #4 buck went through all 4 layers, #5 bird went through 3 layers, and #8 bird went through 2 layers and almost through the 3d. For my own home defense, looks like #5 bird is the one. Your mileage may vary ...