Here's a good list of loads from handloads . com for the big 500. I've used several of these loads in the 500 I got to load for. It belongs to my future son-in-law, but I load his shells for him.
http://www.handloads.com/loaddata/default.asp?Caliber=500%20SqqqW%20Magnum&Source=&Type=Handgun
Click the drop down menu to select "all" to see the 500 loads.
Don't be scared of that revolver. It kicks the most of ANY handgun I ever fired, BUT it did not injure me!
Those pics were while firing the 700 grain grand canyon cast bullets from this mold;
Those bullets were being launched at approximately 1100 fps. We shot about 20 of those that day, no damage to either of our hands OR the revolver. The Simmons red-dot sight however only survived another range session of those loads before failing, got so beat up it wouldn't stay on. Found the battery had dents in it!
Replaced it with a BSA red-dot, then the rings gave up, sheared the claws where it bites into the base!
A set of steel rings has that solved, now it'll probably shear the screws holding the base on.
Notice on that list on handloads dot com that nowhere is Alliant 2400 listed. There has to be a reason for that. My guess is it's too fast for magnum loads, and too slow for lower range loads. I'm sure somebody has tried it, that alone should clue you that it does not work. I'm not going to waste the effort to try it, or waste the powder, bullet and primer. I used W-296 for those 700's and another load was with lil-gun.