The jagged cookie cutter thingy you see on the front of some breaching shotguns is actually a stand-off device. When breaching a metal door you need to have a small amount of stand-off from the door/lock IOT (in order to, military jargon) complete the breach successfully. If you put your muzzle directly against the door you chance jamming the barrel with slag and fragments. Number 2, the "cookie cutter" is an excellent tool for breaching windows and also muzzle tapping your enemy in the chest without clogging the barrel of your beautiful Mossberg. Although not necessary for a proper breach it helps when under stress and your nerves are firing 1 million times a min. With the cookie cutter place the jagged edge against the door, turn the gun till it's at a 45degrees horizontally and 45degrees vertically with the door, pointing away from the door frame. Without the "cookie cutter" all the same except create about 1" of stand off.