Screws used in rifles are in sets: the toe plate screws, the butt plate screws, the tang screws, etc. So the rear most one of each set gets a single cut from a safe-sided triangular file, and so on.
I never remove screws from barrel escutcheons once they are seated, but file off the slot leaving a little countersink head to retain the inlay. Just thought I'd add that. On a Hawken rifle, there are sixteen of these, and that would be a nightmare keeping them separate, especially when one doesn't need to.