.458 brass grows when fired and resized like any other caliber. If the chamber is tight and die is a close match, doesn’t grow much. Chamber sloppy and die is something else, it grows. Remember the the Rcbs X die? It attempted to hold the length static while resizing. It disappeared so the market said it didn’t work. I never used one. The idea had merit though. As a side note, you maybe are trimming needlessly. Certainly are in a Lott chamber but many 458wm will accept brass longer than spec.
