What about trailboss in the 454 cases for plinking? There should be a recommended load on the Hodgson or ADI/Thales site.
http://data.hodgdon.com/cartridge_load.aspHas 7 different loading of Trail Boss from a little over 500 fps to 900 fps or so. Trail Boss is good stuff, I couldn't agree more with his recommendation.
Good Luck,
Mike