Does it actually form a point on the .218 bullet? If not, it is most likely a core swaging die. The early benchrest guys set records with RCBS bullet dies and suggested various improvements to the basic swage die set, including a die to swage the cores to reproducible sizes and weights. RCBS also offered a core seating die.

I would greatly like to see a picture of your RCBS dies. They are pretty uncommon any more.