He developed this method for the following reasons.
1) Eliminate the leading normally associated with firing shot through a rifled barrel.
2) Maximize the shot payload and velocity while maintaining good patterns. I was hoping to include enough shot to equal "typical" boolit weights for these cartridges.
3) Be able to make them entirely myself without any commercial materials other than the normal handloading supplies.
He intended these for revolvers, but I extended the idea to my levergun, as I wanted a good short range grouse load for when hunting hasn't gone the best.
In his own words.
To accomplish this, I decided I'd need to use a plastic "wad" or "shot cup" with petals like modern shotshells use to protect the bore, and the shot cup would need to extend beyond the cartridge brass like a normal boolit to contain as much shot as possible. CCI shot capsules accomplish this, but they are expensive and don't hold nearly the amount of shot that they could. I experimented with many different things, and finally settled upon using 1-gallon milk/water jugs for material as it will melt and form quite nicely without becoming too brittle, and it is self-lubricating and pliable, making it quite suitable for a shot wad. It's also universally considered trash, and is therefore FREE.
This is going to be long on pictures, so I won't include a bunch of pattern shots, but perhaps in a later post if folks want to see.
The .357 Magnum carries 125 grains of #9 shot and fills typing paper up at eight feet from a 4" barrel, with a half-dozen or so pellets off the paper.
The .45 Colt carries 255 grains of #9 shot and fills typing paper at 11 feet from a 7-1/2" barrel with maybe one or two strays outside the sheet.
Zero leading, patch pushed through the bore comes out with just a smudge of powder residue. A cylinder full of these can be fired without any of the shot capsules migrating forward and locking up the works, and I loaded these pretty hot ( equal to same weight of regular boolit with fairly slow powder). The slits down the sides of the shot cup, plus the tendency of the material to want to return to being flat create constant case tension, and the bottom of the shot cup it precisely dimensioned to bind with the case walls at the exact level of the overpowder wad create a good bit of friction with the case. Since straight-walled cases thicken toward the case head it is necessary to predict powder level and make the cup base the correct diameter. For the .45 Colt, there is no need to taper the wad, but the .357 Magnum had to be tapered quite a bit. if you shoot .41 and .44 Magnum skip this and use cushionless .410 wads. .38 Special is a waste of time IMO.
I make these by full-length sizing and priming brass, charging the powder, tamping down an over-powder wad squarely and tightly, pressing the shot wad tightly over the powder wad, installing a support collar over the protruding petals, filling and tamping the shot cup full to 1/16" below the collar, and then melting and forming the petal ends over the shot to make a sealed cap.
The shot cups themselves I make by cutting water jug material with a razor knife and a sheet metal template, wrapping the cutout around the mandrel, sliding the forming collar over the shot cup/mandrel, melting/forming the protruding plastic into a base cup for the shot, removing the mandrel and pushing the shot cup out of the collar and then slitting it down the opposite side of the formed edges to make a two-petal shot cup. In the last pic I put the .45 Colt forming tool with shot cup ready to melt/form the base from the plastic sticking out so I could get the process into one picture.