John;
Can't help you with the RST's but I load STS's with 12.8gr. 20/28, Rem. PT28 wad, AA209, 3/4oz. shot. Check the Alliant website as there are a number of loads for the STS using 20/28 and Unique.
http://www.alliantpowder.com/reloade...l.aspx&shotype