ArmySon - Depending on how much ammo you're buying, I'd stick with #4's and try #2's if you're going for more range. I've never shot the stuff myself, too spendy and I do well enough with steel so I don't bother. My favorite load is a 2-3/4 #3 steel.
You realize that a 3-1/2 #4 has no more range than a 3 in. #4, you're just slinging a denser pattern (and paying more for it!). You'll get more range with #2 and still have a dense shot cone with the 3-1/2 shells. I don't know how well you shoot, but having helped put on waterfowl hunting clinics all over Alaska, I know that most duck hunters 1)can't judge distance worth [color=#FF0000]█[/color][color=#FF0000]█[/color][color=#FF0000]█[/color][color=#FF0000]█[/color][color=#FF0000]█[/color], and #2) can't shoot well beyond 30 yards. When they THINK they can shoot well beyond 30 yards, see #1. What often happens is that people spend way too much on ammo when the problem is not the ammo at all, its shooting ability (and I'm first in line to admit I've been down that road
). Good luck! Hope you slay 'em.
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RKBA!