What you are really looking for is how and where the gun shoots. Knowing the point of impact is critical and many folks are surprised to see how high/low or even left/right their gun shoots especially when shooting at extended range.
Beyond that I agree with the others that you are wasting your time if doing much patterning for waterfowling. For waterfowl I'd say pick a shell thats readily available and fits your budget and pair it with a quality choke and hit the patterning board. No sense buying multiple chokes or loads unless you have money to burn. The pattern will show where the gun shoots and thats that...
Now, if you do as I do and hunt turkeys then patterning becomes a bit more critical. Suddenly striving for patterns like this becomes a useful endeavor..
This post was edited on 7/18 at 1:29 pm