I went out duck hunting today with steel shot and a BP gun, wound up killing a couple of ducks over decoys. It was everything that I could have hoped for. They were both one shot clean kills. I was shooting 100 gr. of pyro RS with 1 1/8-1/4 ounce of shot. I ended up killing a hen GW Teal, and a Hen Mallard (VERY RARE in my area). I have only killed 3 mallards in 7 years of duck hunting so it made the trip that much sweeter.
Best of luck to you all as you go afield with your BP shotguns.