Try a Skychief load, it will surprise you. There is a sticky for it in the smoothbore section over at the M/L Forum.
I have a jug choked 12 that never shot a good turkey pattern until I put a Skychief load in it.
I used 90 gr of 1F and an ounce and a half of #6 shot. This is a Skychief load at 25 yards, the gun shoots a little high, I held on the head.
This is a cylinder bore 20 that shot such a bad pattern that I wouldn't even shoot at a squirrel with it. This is at 20 yards with a Skychief load, 80gr of 1F and 1 1/4 oz shot. The gun shoots left, I was shooting at the center seam, I have never gotten around to bending the barrel.