With a hard alloy you have to load to match or go over by .001.
You can load undersized cast bullets and get them to shoot well, but they have to be soft. Pure lead bullets as small as .427, or 1-2% tin with pure lead, will bump up and shoot well in a .4730 or .431 bore if used with black powder - since the "kick" is sharper with BP. Rifle manufacturers prior to smokeless powder were not overly fussed with bore sizes, hence the variety of bore sizes in old lever guns. If you have an undersized mold or an oversized bore, this is the answer.
I have wondered at the utility of hard alloys, since I have fired a 220 grain .44 bullet of pure lead through 9 water jugs and still didn't get it back. This will catch a .270 bullet but not a soft lead bullet going slow. Sometimes things aren't what you think. Likewise the red deer I shot with the .44-40 were all pass-throughs except for one that stopped in a spinal column. The wound channels were narrow, she just punches a hole through, but the hole does go right through.
