Lyman #454424, 255-260 grs. cast of wheelweight or even slightly softer alloy and 8.5 grs. Unique is a very popular and accurate load. With the large chamber throats of the original guns, .454" is a minimum bullet diameter.

I use an old Lyman mould that casts around .456" or so. I put the bullets through a sizer/lubricator using a .459" bullet size die so they only get lubed and not sized at all.