Stan-
I have seen them in a couple museums in Maryland where the barrels were flattened to make a wider pattern.
Black powder loads suggested included a rag for a wad, and pebbles, nuts, and nail stubs for projectiles.
I have a scull boat here, and when I was sculling regularly, it was no difficulty getting alongside a raft. (L,S,&B BrantII) Open water ducks just aren't super wary.
There are some sculling videos on youtube.
I like it because you can "Spot and Stalk" your quarry.
I haven't re-read this thread, but also remember that this style of gunning was performed to great effect in the SPRING, just another reason it was outlawed.