Forget the patch. Try a greased 550 over one or two 1/8" felt waddings followed by an overshot card. You might also try just a tight o/s card instead of the wadding, sometimes that works well too.
I go up one bore size with my waddings and os cards as tighter is better...to a point. Most smoothbores I've owned shot as accurately loaded this way as with a prb at traditional smoothbore ranges, generally 60 yds and in when the proper powder load is found.
The nice part is the utility and ability to shoot shot or prb. The 56 is a good little caliber for small game and turkey to about 20 yds with shot and out to about 60 with round ball.