They don t understand what is involved, what to look for, and how important it is to their shooting success. Many people will shoot a load, one time, at a cardboard target, look at it, and say, Okay, I patterned my shotgun . They draw a 30 circle on the target, and count the number of pellet strikes within the circle. They can then figure what the percentage is for that particular load, in that particular barrel.
Patterns are all about quality.
The worse one, on the right, would have a very strong core density and a weak fringe density. A poor pattern will also have relatively more vacant patches, or areas void of pellet strikes within the 30-inch circle. A high quality pattern will have few such patches. Both these prints are reprinted by permission of Melvin Marcher of Oklahoma City, OK, from the book The Mysteries of Shotgun Patterns. The history of patterning.