I also have shot a ton of the shot capsules in both the 38/357's and the 44. Like mentioned finding the proper crimp setting is the hardest part.
I loaded my own shotshells for year as well so had a decent supply of shot around to play with. I have used from #4 up through the tiny #9, and found that around size 4 or 6 seemed to work out the best with my loads.
With the 44's I also used two of the Speer .350" lead round balls with a couple of pieces of felt on the backside to fill space and cushion them. These would strike about an inch or so apart out from my 7 1/2" Redhawk to around 25 or so yards, and were a hoot to hunt rabbits with. The thickness of the felt will determine how many are needed, you just want to be sure they are good and tight when you shove the plug in. I used a .357 case with the outside of the mouth chamfered sharp with a file to cut the felt for a perfect fit in the capsules.