I think the .500 S&W has a bore dia. of .500-.501, the old .50 cal. blackpowder rounds are .512+/-.
If you just want to shoot blackpowder, just find some lead bullets to fit w/ the correct alloy and load away. You can load that case w/ b-powder
http://www.montanabulletworks.com/wst_page6.htmlIf you do, talk to these guys about an alloy of 20-1 or 30-1, a light bullet would be good for a deer hunting load. Good Luck.
If you decide to load some B-P, try to find one of these "BP Reloading Primers"
http://www.blackpowderspg.com/mlvbooks.htmlThis book has all the info. you will ever need to load any B-P cartridge, it doesn't show every combination, but also shows how to figure out loading any bullet and powder combination.
I think its a required book for B-P shooting.