357/38 Powder choice

[severnsider]

Totally new to reloading but having looked at factory ammo prices I bought a s/h Lee set-up with literally everything I need apart from powder.
The thing is I've got some Herco powder I want to use but not sure what amount of powder to use? I have a Rossi 357/38 btw and 158 lead or jacketed heads available.
I just need some safe loads for both calibres if anyone can help please.

Lee Modern Reloading suggests 7.1 to 7.9 gr Herco with 158gr lead in .357 and 4.0 to 4.5gr in .38SPL. No data on the Alliant site for 158gr lead,
The Rossi has a slow twist, 1:30". You might find that it prefers a lighter bullet? I have achieved good results with 125gr lead (truncated cone) and 4.6gr N320 powder in .38 cases; 6gr Unique with 158gr RN in .357 cases also worked OK. I've not used the N320 in .357 cases yet.