A shotgun blast is made of many small pellets. Knowing how those pellets behave in air and what their "pattern" looks like when they make impact from different distances can give you the edge on shotgun accuracy and efficiency. Unless you have patterned your gun and shot some clays at different ranges, you simply can't know how your gun is performing.
If you intend on shooting both steel and lead shot, patterning your gun with the various loads and choke options is easy.
Shoot pattern boards or targets at five-metre intervals, from 20 to 60 meters, to see what the pellets are doing. Most patterning targets are printed in the U.S. with a 0.762 metres (30-inch) diameter circle as the critical zone. The goal is to fill the circle with evenly spaced pellets for the best performance and pattern.
Example: You shoot a load of steel BB at your target, and there are 65 pellet holes in the inside the circle and five pellet holes outside for a total pellet count of 70.
65 divided by 70 = .928 x 100 = 92.8% effective pattern
Shoot at least three patterns with the same make and pellet size of shotshells. So if you're trying a 3-inch No. 2 steel load, shoot at least three to check for consistency.
If the pellets are clustered and not spreading properly, you may have to go to a more open choke.
Most steel will shoot well through a modified choke. If your patterns are inconsistent or not grouping properly, try an improved cylinder or skeet choke.
Every gun patterns differently, so try a variety of shotshell manufacturers. If you pattern guns with friends, you can split up boxes of shells and try many different loads.
Shooting rests can save you from the heavy recoil of magnum loads and give you a true picture of what your shotgun is doing. The rests hold the shotgun firmly in place so you can dial in the windage and elevation shooter error in your tests.
Just remember, the time spent getting to know your shotgun will pay for itself with confidence and success in the field.