Have not loaded for the 50, but have loaded for the 44.

I have had good luck with both N-110 and H-110 powders. I get roughly the same velocity with each, but the H-110 is much more loud and flashy. I use Zero 44 JSP bullets, but unfortunately they don't make a 50 bullet. I have a friend that has used the Berrys bullets for his 500 S&W, but I don't think he pushes them very hard. You don't have as much leeway with an auto-loader, though, as they have to be hot enough to cycle the action.