The round balls I've cast were mostly .490" and the Lyman mould did cast a prettier ball. The Lee mould liked to show winkles but both cast good consistent balls, IIRC
The iron moulds hold heat better and, unless you've got the lead REAL hot and are casting fast, IME, an aluminum mold can be a bit fussy. ...But, I'm not the best caster so it could have been something I did/did not do.
"Much learning doth make thee mad" - Festus