I picked up a 4 lb. jug of Alliant Steel powder several years ago because I got a deal on it and most shot gun powders work fine in pistols. Steel falls in between Blue Dot and 2400 in burning rate so it is in a good range for large magnums. Steel is low desnisty bulky powder and should be easy to ignite so I figured it would be fine for medium level loads.
I had tried it before in my .44 Mag but not in a .500 so today I loaded up some Steel powder behind some 440 gr. gr GC bullets I had cast up. I tried 20, 22, 26, and 28 grs based on loads for similar powder. Didn't get to chrono these but they seemed to shoot fine with no signs of excess pressure.
After loading them I also relaized that I had mistakely used large pistol primers in Star cases made for LR primers. Happy to say no misfires and everything worked fine. This was in a 4" S&W - results may vary with other guns.
I'll post more as I work with this powder - I think it has good promise for medium loads in the large magnum pistols.