RE: how do you count patterns
Hmmmm... well, first I'd shoot at a target, then I guess I'd walk up there, then go, "1... 2... 3... 4 " Ok, ok, I'm sorry, I just couldn't resist. [8D]
Seriuosly, the 10" (or 12") circle method is likely the most accepted method for patterning turkey loads. Your goal is to find the most concentrated area of your guns payload at your given hunting distance with the choke / shell combination that works best in your gun. No two guns are the same, so a bit of trial and error with different shot sizes and choke constrictions is probably going to be necessary to achieve the best results.
Another pellet count / patterning method would be to pattern your gun using a 30" target. Check to be certain that your gun is hitting point of aim, fire at the center and then count the number of pellets in that 30" circle. Dividing the 30" circle into 4 quadrants will help you obtain an accurate pellet count.
Now, take the manufactures number of pellets published for the shell that you just shot and compare it to the actual number of hits on your 30" target. This will allow you to calculate the percentage of hits within the given target size for that particular load fired from your gun.
I employ both these methods at once... in that drawing a 10" circle within the 30" circle gives me the data collection for both of the above, after firing only one shot. You can use the turkey target within this same 30" circle too, allowing you to view hits to the brain / spine area of the bird, while giving you an overview on how well the pattern stayed togther surrounding the turkey head target. You can use these targets later to compare groups of pellets, which will help you choose the right choke, (tighter or more open), to dial in the shells you prefer for turkey hunting.
Take some time and remember to clean your barrel after each round of 5 shots. Remove all oil / gun lube and plastic fouling. Failing to do so will degrade your shot pattern and yield less than what the actual combo is capable of. Patterning can be time consuming, but it's fun too.
Another side benefit from all this work is that you become much better with your gun. The confidence alone in that the shot you are about to take is one you can make. It's a great sport and we all owe the bird that much.