I have used my cast bullet for the 44WCF for quite a while now and I keep them at 9-10 . You have shooters giving you the different numbers but it's important to know how they load and what they shoot. I shoot full case loads of 2F and my bullets give a perfect seal. If someone shoots 38 spl with a mouse fart load, they will not have much blow by. A person who shoots 45 Colt with full loads of real BP not only needs a soft bullet but you should anneal your case necks to soften the brass and stop most of the blow by.
You can't compare the play like powders with shooting the real thing as the two don't burn alike.
Paul Matthews has written several books that are good reading for a person interested in shooting the real powder. The lube you use is very important for good sealing, accuracy, clean up. I use NASA. Take Care Fairshake