Re: New Guy Needs Help on Neck Turning 308/223
Think of neck-turning as fitting the brass to a tight chamber; perfect clearance. The other benefit is consistent neck wall thickness. Many these days find that they can do as well with excellent brass (Lapua) in a no-turn chamber.
I suggest that you read Glen Zediker's "Reloading for Competition", available from Sinclair. He goes into great depth in explaining brass preparation.