I guess you have a 32 special?
Yes, use cast bullets that are .322" or .323".
The 32 special is one of those cartridges (like 45-70 and 30-30) where you can safely use jacketed bullet data for cast bullets. Everything else being equal, cast bullets have less friction and will shoot at lower pressure than jacketed bullets of the same weight. The velocity limit for cast bullets is not a "safety" issue, but that too much speed could cause the cast bullet to start leaving lead in the bore. I find that it usually works very well in these cartridges to use the starting load for jacketed bullets of the same weight and keep velocity under 2000 fps.
Shooting cast also works much better if you give the barrel a good scrub before starting with cast. Removing the traces of old copper jacket material helps cast bullets shoot much cleaner.