I've loaded the .44 Speer shot capsules into .44 Special cases, I used Red Dot powder but I can't recall the exact charge weight. I DO remember that it was a very light load, the more powder I used, the more screwed up the patterns got.
I was using the load to kill rats around our barn, the greatest improvement in effectivness came when I purchased a box of 12 gauge shells loaded with #12 shot. I cut a few open, loaded up the #12s and almost doubled the number of kills I made per shot compared to the #9s I had been using. It's a whole lot easier on the barns structural integrity as well.
Swampman