Pete, I'm not sure what your fired 30-30 cases measure right ahead of the rim, but most 30-30 cases run about .422-ish. The old 25 Remington cases are about .421 right ahead of the rim.....so maybe a 25 Rem. f.l. die could help out if you just need a thou. right ahead of the rim. If so, you could just open up the forward part of the die and use it as a 'ring' die to size the area just ahead of the rim. But if you need to 'small base size' much of the 30-30's taper, this might not work as the 25 Remington cases don't have the taper that the 30-30's do.
For what it's worth.... -Al