Depending on your particular pistol and what it will chamber you may not need to size the bullets much at all, my CANIK TP9SA feeds an shoots the most accurately with my cast lead bullets sized to .357". There are lots of factory sub-sonic loads out there in the 158 gr. range these days for suppressed 9mm handguns and carbines so the bullet weight is not really an issues. Lots of tired and true info out there on loading 158 gr. cast loads in the 9mm, just Google 158 gr. 9mm loads.
Here is a pretty good read on the subject.
http://www.shootingtimes.com/editori...mm-luger/99514