Yep, alot of the "rules" don't aply for cast bullets. I usually full length resize any brass that hasn't been used with cast first, then usually home free.
I had much better results with cast in 30-06 by running the neck up on the deprimer stem of a .303 brit neck size die (just the first 3/4" into the die, you know). Guess it would be mostly like using a Lyman "M" die to expand the diameter a little more - the regular RCBS just crushes it down too much for cast. May just have to break down and buy some "M" dies.