Re: Neck sizeing vs. full length?
Uh oh, don't flame me - factory barrels for the most part (not all factory chambers). If I haven't said it before then allow me to reiterate a point I make often: neither my rifles nor I could discern any significant advantage betwixt NS and FL sizing based on results on the target. What I was referring to was overall concentricity; my Hornady and (not mine) Sinclair concentricity tools have repeatedly indicated FL sizing to be yielding straighter rounds. The one exception to this, within margin for error, is the Lee collet die, oddly.
And to restate a point I made a few posts above, accuracy is achieved through many factors other than the way you size your brass. I wouldn't dare presume one method better than another for anyone else; as long as they find combinations of production, tools, and components that end up with the results they want. There's methods that are better for me and there's methods that are better for you.
But if you're asking me this because you haven't measured runout on your assembled rounds and just want an idea of what you could expect, then my answer in order of most concentric to least (when only taking into consideration sizing, and based only on my experience with the tools I have at my disposal): FL sizing, Lee Collet, NS & fireformed / NS & Body die. This assumes everything else being equal, including how you prep, trim, handle, clean, seat, crimp, and store your ammo and which position Neptune resides compared to Jupiter's 12th moon. Even a different batch of bullets will change this reading dramatically, more so than how you size. In like, the difference between FL only and NS only might be .001" - we're splitting hairs here. Very few rifles exist that could take advantage of that sort of difference, and even fewer people talented enough to shoot it.