I would use a modified choke, I.C. is going to be a large pattern good for 15..20 yards w/ a 20ga and 5 or 6 steel shot. Modified will stretch that another 10..15 yards. You really need to take a few shots and see what kind of pattern you get at various distances. Where I hunt in N.H. we tend to use full choke and larger shot on waterfowl. 12ga also. I have some #2 Black cloud for my sons 20ga Modified, works very well. But, distance is everything. Over 25..30 yards, it is useless. Patterns are so big all you may do is injure the bird.
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