The task of patterning a shotgun has become somewhat of a lost art. But it is an essential part of understanding how the gun will work with the varying shell velocities and shot sizes which make shotguns such a versatile option for home defense.
The most important variable that must be taken into account is that the further the shot has to travel, the more disbursed the pattern will be. In a home defense scenario, 10 to 20 feet would probably be the maximum distance the average home would afford. At those distances, the shot pattern would be from 2 to 6 inches, which makes the need for an aimed shot far more essential than the common myth about shotguns would suggest.
The common myth is, "you don't have to aim a shotgun. Just point it in the general direction and pull the trigger." Nothing could be further from the truth. On the contrary, the truth is that distance, the velocity of the shell charge, and the size of the shot all work together differently through different guns causing variations in the shot pattern. So understanding how YOUR shotgun and ammunition work together is so important to proper use as a home defense tool.
This video, provided by the National Shooting Sports Foundation (NSSF), does a great job demonstrating how important shot patterning is and how to do it.