The greater the constriction, the greater the degree of spreader effect. Thus, you see relatively more opening through Full than through IC. The spreader through IC may well throw the more open pattern.
When I've loaded cardboard X and plastic polywad discs the opening can reach true cylinder (40%) and result in pattern voids at even 20 yds. Most here already know that shotcup loads through .000 don't often give patterns as open as 40% (.410 excepted). Mike Campbell writes (on 16ga.com and UPJ) about a shot-layering technique that places about 1/8 oz shot on top of the disc. I have tried this approach in both 16 and 12 ga and found it works like a charm. Pretty easy to do. My search-fu is not working this AM, but if you dig through those forums you can find his excellent, detailed posts with pics.
Another approach that works - sometimes - is to use soft shot and soda straw inserts. It gives me LM patterns through my .021 16 ga M12.
I bought some Polywad factory spreader loads for the kid's .020/.020 ASE90. I've been pleasantly surprised to find useable open patterns suitable for the close rabbits.
Sam
