I can't give you a Magic Number, I think gradually honing out a hole is the best approach for a homemade die. Here are some posts by a guy who worked on it a good deal. Note that he was loading fresh cases, not reloading to have to size or deal with the aggravation of repriming the rim. And he (they) were loading black powder which might be more fun than you care to try.
http://www.shilohrifle.com/forums/vi...hp?f=5&t=16806
http://www.shilohrifle.com/forums/vi...218970#p218970
https://castboolits.gunloads.com/sho...hlight=rimfire
https://castboolits.gunloads.com/sho...er#post2619658
https://castboolits.gunloads.com/sho...46-22-lr-bpcr-!!