The 500 S&W Special is a shorter-cased version of the 500 S&W developed by Cor-Bon/Glaser (at Smith & Wesson's request).
It is no different in concept from a .38 Special fired in a .357 Magnum, or a .44 Special in a .44 Magnum. Two loads are currently available-a 350-grain JHP at 1,350 fps/1,417 ft.-lb., and a 350-grain full-metal-jacket "plinking/practice" round at 1,300 fps.
If you reload, they make no sense at all.
You can accomplish the same ballistics and reduced recoil using normal .500 S&W cases and jacketed bullet starting loads from any reloading manual. Or even lighter plinking loads using lead bullets.
(Without the nuisance & bother of the shorter cases fouling the chambers like .38 in a .357 requiring a lot of extra cleaning time before you can shoot full power loads again. Or the added expense of .500 Special cases.)
BTW: I think S&W may have had some ulterior motive in developing a short case instead of just loading a light practice load in standard cases. The .500 Special loads are still Magnum power by any stretch of the term Magnum.
I think at some point they may introduce a smaller .500 Special revolver that would not require quite the massive size & weight of the X-Frame .500 Magnum.
rc