Running a bullet slightly smaller than cyl throat is not an issue vs running a bullet the proper size thru a smaller cyl throat. If you want to run 0,431" bullets, the slightly larger throat doesn't usually present an issue.
BTW, putting gc on bullets almost removes the issue. The gc will act like a jacketed base & grab rifling. Leading may or may not be an issue depending on the final bullet size as it passes thru the cyl throat.

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NRA Cert. Inst. IDPA CSO