Re: Neck Size vs Full length size
The straightest and most consistent your cases ever are, is as pulled smoking from the chamber.
Anything you do to them from that point changes this, so it is best to do as little as possible. It is rarely good to FL size cases with factory dies, -until you have no choice. .
Ideally you wouldn't have to touch formed cases with a die to reload them, and still have easy bolt closure. This would certainly produce very straight ammo.
But your particular chamber, cartridge, and load drives this.
I use JLC bushing/bump dies for several guns, but I don't compete. I just want straight brass that lasts. If I were shooting a 6PPC, 30BR, or a 6.5UnderPowered as fast as I could between conditions, and at extreme pressures, then I might FL size everytime.. I don't know.
With my cartridges I partial NS, and see no reason for tension beyond the seated bullet bearing. I bump shoulders as needed, that's it.
My ammo is very straight, lasts a long time.
My setup in 223 is the simplest/least expensive. Here I use a Redding body die for slight bumping about every 5th reload. Wilson neck & seater dies, and I run a Sinclair carbide mandrel through each neck prior to seating.
Such an easy cartridge