Lymans 49th has some "reduced" loads using Unique powder. I haven't tried them yet, but i might since I can only shoot a few cylinders worth of rounds using H110 before the frame and barrel get too hot to touch and nobodies got time for that.
Do you mean load a "light weight" bullet or a "low power" load?
If low power: 13.5gr/Unique with Berry's 350gr plated RNFP. COAL @ 1.970", taper crimped. I use CCI-200 primers but CCI-300 work fine with reduced loads. Usually go with 15.0gr or 17.0gr/Unique though. Loaded cost/round: <$35/100
I just bought some of Acme's 330gr L-RNFP HT-coated bullets but haven't gotten to the range yet to try them with the above loads.
I load 300gr JSP IMI 50AE bullets for my 500 using 17.4 grains of unique.I also load 325gr Speer JHP 50AE bullets using the same charge. Both are pretty accurate. But they are not a light load. More of a mid range load.
For light loads I use the same bullets with a case of 90-95% full of Trailboss. You don't want to compress trailboss, it will break the little donuts. Which is a no-no. But those are light loads out of the big 500. I'm gonna try some Rainiers lead free bullets sometime. They should work well with the Trailboss.
I wish I had access to a chronograph to check velocities on these loads.
As always work up your loads slowly and use reloading manuals as a guide. I would never exceed max recommendations and rarely load hot loads anyway. If you need more power switch powders.
You could try 15.0 grains of HS-6 behind a 440 grain cast that will get you 930 fps from a 5 inch barrel and should be accurate in about any 500 Smith.