I have an rcbs fl die set for .308 and I don't know why I am unable to get die set to just neck size. That is what i do with other calibers, but have not been able to just size the neck on my .308. I usually end up having to partially size the case. I am planning on ordering a lee collet die though. Also I have herd that FL resizing is necessary after around 3 firings is this true?