The classic .32-20 cast bullet is Lyman #3118, a 115 grain flat point. Factory .32-20 bullets, both lead and jacketed, ranged from 100 to 125 grains, so anything in that range is appropriate. Several commercial casters sell bullets very similar to the 3118 which, as mentioned above, is now cataloged as the 311008 due to Lyman's revised numbering system.
Other Lyman bullets similar to the 3118 are 31133, a 100 grain FP, and 311316, which is basically a 3118 with a gas check. Gas checks are not needed with .32-20. The best .32-20 jacketed bullet was the Remington 100 gr. JSP, which has not been made for probably 30 years unfortunately. I used many of them in .32 S&W Long in my K-32. There are really no current jacketed bullets that are appropriate for .32-20. I have seen Lyman 3117 mentioned in this and another thread. There is no Lyman mold with that number!
Because of the long-for-caliber case .32-20 tends to produce squibs if used with powders that create small volume charges. To prevent this use bulkier powders that fill the case better. Unique is pretty well the best powder over-all for this cartridge in revolver and rifle. With the current state of Unique anything in the same burning rate range should work well. Do not use Bullseye, 231, etc. because of the small volume charges and possible squibbing and subsequent barrel damage from bulges! I use Small Rifle primers in all .32-20 ammunition as this reduces the chances of squibs!!! If you do happen to bulge a barrel in a .32-20, rifle or revolver, remember, you were told!
I have been loading .32-20 for both rifle and revolver since ca. 1962. All my comments are based on my own experience, personal and professional, with this cartridge over those 60+ years. I have seen many .32-20 guns with bulged barrels caused by squibs!
Overall my best luck with cast bullets in .32-20 or .32 S&W Long is size them .314" to .315". I use Saeco Green bullet lube for all cast bullets as it is by a wide margin the best of many I have tried in preventing leading with cast bullets, including LBT Blue Angel and numerous other other "boutique" (read expensive!) lubes that are supposed to be so good. They aren't! I cast all of my own bullets in nearly 100 different styles. All of my molds are from Lyman, Accurate Molds and RCBS, and in calibers from .22 to 20 gauge, .625".