You may have a difficult time finding loads for what you are looking for. For a Number 2 alloy, 230 grain LRN bullet, Sized .452 the Tightgroup load is as follows:

4.0 to 4.8 grains gives 751 to 855 fps at 12,500 to 17,000 cup. I believe you would need a FMJ or at least a gas checked bullet to keep the lead from melting with a really hot load.

Have never seen loading information for a 255 grain bullet except for rifle loads.