Before you get wrapped around the axle...
measure the chamber mouths of your cylinder. Many of the original .455 revolvers I've measured (and the one I shoot all the time) have chamber mouths which measure around .450" - .451", and the groove diameters are around .453". There is no advantage in squeezing a very large bullet through a tight chamber mouth, and I find that the standard .452" .45 bullets shoot very well, indeed. I like the 255 gr. moly-coated RN hard cast bullets, which shoot very well, indeed.
PRD1 - mhb - Mike