My Forsters have a .490" or so cutter, so would slide inside a .500" case mouth.
I couldn't quickly locate my Lyman, but the RCBS's cutter was about .577" dia.
Maybe it's time for me to get a ¾" piloted countersink for use in a drill press for my Snider cases.
I guess they could be sized small for trimming, then opened out and anealed for loading.
Cheers from Darkest California,
Ross