This video documented a ballistic test using a 20 gauge Remington, Model 870 firing at a standard designed panel assembly at 50 ft.  The cartridge was a Remington 2 3/4 length, 1250 FPS, 7/8 oz shot, 7 1/2 shot Game Load.  See for yourself if the shot penetrates the wall.  Optional Kevlar plies may be added to stop rifle bullets.  All rifle ballistic tests should be performed on specific variable kevlar thicknesses built in the panel assembly before enclosure ordering, call for test arrangements.