Re: Brass headspace question
Brass only "grows" when it is stretched so far that it can't spring back to its original dimensions. Lee collet die only sizes the neck, it doesn't touch the body. The Rem and WW case where probably different lengths to start with.
Bump the powder charge up if not stretching the brass is really a concern. If it is shooting up to your standards I wouldn't worry about it. Folks spend lots of time and money for tight chambers/custom dies/etc. to have brass that doesn't need, or only needs minimal, re-sizing.