Patterning Your Shotgun
No two shotguns or chokes, even from the same manufacturer, will shoot identical pellet patterns. In some cases, the pattern will be off-center. In other instances, there may be gaps in the pattern. In addition to the firing characteristics of the gun, the gun’s choke, the brand of shotshell, the shot size, and the type of shot also affect the pattern. In order to select ammunition that provides the best performance, it’s necessary to "pattern" your shotgun.
Shots at game birds in flight should be limited to your "maximum effective range." This is the distance at which you can hit the target consistently. Shooting beyond this distance leads to an increased number of birds wounded and lost. Also, firing at game too close to you may destroy the meat. If the pattern is unacceptable, try a different brand of ammunition, choke, or shot size.