My copy of the Alliant Powder RELOADERS' GUIDE , is the 2000 version. That is where I found the 2400 load i mentioned.
I checked <wwwalliantpowder.com> I only found RL7 and RL10X listed for .444 loads.
My 1973 version of the Lyman CAST BULLET HANDBOOK lists several loads with available shotgun powders, most of which acheived your target velocity. Stan Waters' PET LOADS focussed on getting top velocities for jacketed hunting bullets, IN THE MARLIN. No testing was done for cast bullets or lower velocity. (His conclusion for top performance was narrowed down to one powder, 4198!)