Not sure I have any secret, but I'll tell you the load configuration that I ended up with:
28" - .62cal (.20ga) smoothbore barrel
70grns Goex FFFg
1st prelubed Oxyoke wonderwad
Over powder card
2nd prelubed Oxyoke wonderwad
Paper shot cup
1+5/8ozs #6's
Over shot card
Prime and shoot
For me, #6's tightened up the pattern a lot as the heavier the shot the better they tend to keep boring more straight ahead than lighter shot;
(To avoid tearing up smaller game and/or at closer ranges, use less shot, or just a shorter cup with the same amount of shot so some of the shot is above the cup and starts to spread more quickly).
I make my paper shot cups from post-it notes rolled around a .5" dowel that's been built up with a few layers of tape. You want the finished cup to have about .020" clearance all around it when it's held inside the bore, so it has room to expand and split at ignition setback time.
Post it notes don't require any glue due to their tacky edge, and when rolled around a properly built up dowel, they will stop just short of two complete revolutions, leaving a narrow strip of only a single thickness of paper which aids in bursting at setback time.
Just fold one end in tight and crease it like you would rolling a roll of coins, slide it off the dowel, pour in the amount of shot you want to use and cut off the excess paper...you now have a custom shot cup for the amount of shot you're going to use...they work perfectly.
Just set the second wonderwad down the bore a couple inches, set the shot cup down on it, pour in the shot, install the OS card, and gently seat the whole thing, being careful not to crush and
burst the cup prematurely by applying too much pressure **.
(** This is just my opinion not to prematurely burst the cup, it's not based on any science...
mine work perfectly for me so: if it ain't broke don't fix it, etc)
And the height of the paper must be no taller than the amount of shot that you're using or the excess will fold over when you seat it, and cause inconsistent separation & shot column disruption from shot to shot. Plus, if you fold over too much excess, the whole thing goes all the way to the target like a slug !!
The cup should immediately flare, shred, and flutter to the ground literally within 5 feet of the muzzle.
Give it a try...