About 10 years ago I shot in one of my favorite two day annual shoots and only had 4 misses two of which were shotgun fallers that failed to go down. At a second annual I could not bring any of the fallers down on the first stage with repeated hits and an 80 gr BP 1 1/8oz load. Fortunately, we were the first posse and I was one of the first to shoot it and the RO reset the fallers to a lighter setting but that was intimidating to me to not blow them over. Lots of smoke and noise but no "umph". This was before much standardization of target size & distance; they were heavy and out there a ways. So I went on a quest to improve the patterns in my cut down (cyl/cyl) Stevens 311. BlackJack Traven on the old CAS-L (earliest CAS Email bulletin board I know of) suggested STEEL SHOT CUPS as he related a similar story. I tried them with extensive patterning tests and have not had problems with knockdowns since. Ballistics Products is my source for the wads.
First of all, the WAA12R (AA Red Wad or Claybusters generic equivalent CB 1138-12) is a very versitile wad for CHOKED guns. You can adapt any AA wad and several other types of plastic one piece wads to 2 or 3 heights by merely slicing out the "legs":
-Cut them out entirely (shortest wad column i.e. over powder seal & shot cup)
-Cutting the "legs" across the middle and rotating the wad 90 degrees and pressing the parts together for a medium high wad
-leave it intact for the tallest wad column.
There you go: a "3 sizes fits all" wad for light or heavy loads in the same or different hulls.
In order to get tighter patterns from my 311 and my TTN, I use 3 different Ballistic Products wads:
LBC-50 trimmed with tin snips to 30mm and slit twice full length. (I use a utility knife/box cutter)
CSD 118 also trimmed & slit twice
BP12 TUFF steel shot cup slit twice over any kind of salvaged over powder plastic gas seal wad
I tried not slitting the wads but they tumbled and threw elongated irregular patterns with about 1/3 of the shot load traveling backwards still inside the cup. I used 4 slits half length without improvement in the patterns. I used 75-80 grs FFg and 1 1/8oz shot as my load. My patterning board was an IPSC target or a large cardboard box with a sheet of freezer paper stapled to it at about 20 yards. Mark an aiming point on the paper. You can use 10 or 15 yards distance too. I think a full choke pattern is 10 inches in diameter at 10 yards but check a shotgun reloading manual for the various widths of patterns expected at various yardages for the equivalent choke. I cannot overestimate the importance of this simple patterning. You may find your gun shoots high, low, or God knows where til you see where the center of that pattern hits compared to where your aimed. I found that I was having some misses on stationary targets with an IGA Coachgun because the barrels were "walleyed" (left barrel hit low & left, right barrel hit high & right).
Results: all 3 above wads threw nice, even MODIFIED CHOKE patterns from my cylinder bores.
I now have essentially two loads. A light "gamer" load equivalent to a 20 ga of 55grs BP (or ANY sub other than 777) with 7/8oz of #8 or #9 shot using any wad column that allows a decent crimp. I usually try to use a plastic gas seal (PGS) OP wad and after that, anything goes: fiber, plastic, cards etc. The light load is for those ever increasing stationary targets and swingers, or fallers so close that any reasonable hit will take them down. I load the light loads in green hulls. My heavier, steel shot cup load is put into red hulls. I can essentially change chokes by changing ammo.
Now, as DGB#29 (that's Dirty Gamey Bastard #29) I also will load custom loads for specific conditions. A big load of wide pattern (no shot cup at all but a PGS+Filler) with 80grs powder and 1 1/8os shot comes in handy. I'll use #9s for the pop up soda cans and briquets and #6s for the times when I think I can get more than one faller per shot when they're placed closer together. I've occasionally gotten 3 down with one shot. This usually happens with the full intent of the stage writer to let shooters "game it" by leaning over or doing whatever to see if they can get some doubles. It's a major fun factor.
So, you've got a hard little knockdown that throws up a can of pop. Left barrel gets a red round and the right gets the wide #9s. Just as if I had chokes, I shoot the tight load first to drop the faller and the open bore for the flyer. It's just like hunting, you have different loads for different critters close or far.
Keep in mind that BP doesn't throw shot as fast as smokeless powder. The short coach guns throw out a lot of unburned powder compared to a 30" gun. The slower to burn BP likes a long barrel to burn it all for maximum velocity. With smokeless, the powder is all burned in the first 18-20" of barrel. So, you are shooting softer loads to begin with. Just to get the equivalent of a standard 3 dram 1 1/8oz trap load you need to go to 82 grs of black. A lot of folks are shooting 55-60grs BP in a 12 ga. That's slow. In order to make up for the velocity lack you need a tight pattern. That's why I like the steel shot cups to put choke where it's needed to blow down the big steel.