Re: Do you need to size brand new cases?
My CZ rifles have match grade chambers and a FL sizing die barely sizes them down at all after firing. If the case is tight in the die when new, then it needs to be resized. If not, and it fits in the chamber, then load up the case and fireform it, provided it isn't over max trim length.
One thing you might need to do to new cases is to anneal them, if it hasn't already been done.
If new cases are oversize and need to be resized, then polishing them will allow them to be resized much easier, with reduced case lube and no chance of oil dents.