I have 3 1858's and just purchased another one in stainless. IMPO you should strip the gun down for a through cleaning. Some new guns are very clean while others may have grit or filings inside from machining. Unless there are obvious large burrs I don't believe in stoning and polishing new parts. If you shoot a lot they will wear in to a proper mating. No need to impose premature wear on your new gun. Disassembly is not hard. Follow the advice given by others in this thread.
So I guess if you shoot one enough, it'll end up with perfect timing instead of worse timing, positive trigger engagement (longevity and safety), a 2.5 - 3lb trigger pull, 4lb hammer draw, develop a bolt block and an action stop ( to "stop" wear from happening) . . . just like the Pietta I had in possession that shaved the hammer cam off in less than 50 cycles? Fitting parts is "premature wear"? Hmmm . . .
Mike