My Son's Mossberg Super Mini Bantam with SumToy, only has 18.5" barrel.... Wads go only 20 yards. However I'm not happy with the pattern either. I've shot Ninja and Federal. I did a deep clean on the barrel again and will try it again. There is no way we can shoot to 40 yards.
I will try a more open choke or tighter... Got to get it right before next year. I believe I will also be using Nitro. They are amazing in my 12's.... Been shooting heavyshot since 2007.