I don't know what chokes you are currently using, but they are probably not that far off. I personally favor open chokes for all my field work, with a few exceptions. The true purpose of chokes is to develop a 70%, 30 inch pattern at different ranges. As a generalization, Cyl at 20, IC at 25, M at 30, IM at 35 and F at 40. These are only generalizations, as the percentages will vary. The problem with the 30 inch pattern is that only the central 20 to 24 inch portion can be counted on to reliably kill. The outer protion of the pattern is generally too thin to consistantly put sufficient pellets into the vital areas of a bird.
Another general rule to follow is that a choke is usually most effective 5 yards before and 10 yards after its' intended range. For example, the IC that is optimal at 25 yards is almost equally effective at 20 to 35 yards. Actually, IC tends to hold together a little longer than most of the other chokes, as Brister proved.
The bottom line here is to figure out the range where you are shooting at most of your birds. Once you've doen that, select the choke accordingly. When you have the choke, pick the pellet size needed to deliver 1.5 ftlbs of remaining energy at 10 yards past your selected range. Select your payload by figuring out how many ounces of your selected pellet size will gice you about 300 pellets in the total load. That will ensure that you get about 130 in the 30 inch circle at 10 yards beyond your optimum range. That's all there is to it! :wink:
One last thing to consider. Once you've selected your choke, get some target loads and get your self to a skeet range. Try practicing the swing through method of shooting, as it is probably most effective for field use inside of 40 yards. You may also want to check your gun fit and make sure it shoots where you look. Concentrate on the bird's head instead of those distracting, long tail feathers.