bkraft,
If it were me, I would put your dad's gun away, and go buy an 870 Rem or some other inexpensive shotgun (pawn shops will be full of them after duck season)if your just getting into shooting ducks. Most will have screw in chokes that will take steel shot or any other kind of shot. If your dad's 20 is 2 3/4" chamber your not going to get much powder or shot. But if you must use it, I would shoot Kent Tungsten Matrix as it will not hurt your Mod and Full gun, and it patterns close to lead. It is costly, but if you can work them in to your decoy spread, be patient, limit your max range to 30 yards or so your 20 will kill ducks. Also you don't need larger size shot. Kent TM #5's work well for me in various 20ga guns I own. Before we had to go to non toxic shot I used #5 and #6 lead on ducks. Season opened here (Arkansas) today. We have the water, but the weather up north has not pushed the Mallards and Pintails down here yet. Our best hunting here is usually in January if the temp does not get too cold and turn the water into ice. Good luck to you sir.
G2
