I've been reloading for 30 years, pistol and rifle (.22Hornet, .223Rem., 6.8SPC, .270) and would like to branch out beyond the typical reloading (plinking/nominal accuracy improvement) and standard reloading dies (Lyman/Hornady).  Maybe something allowing a little more accuracy.  Therefore, I was considering buying a commercial bolt-action 6.5 Creedmoor rifle.  I'm not intending to compete or shoot at 1000yds, but I would like to do the best I can without being anal and buying custom dies.  For the first time, I thought I would try using a sizing-die employing a neck bushing.

1)  If the bullet is .264", brass neck thickness is .013 - .015, and I want .001" neck tension, do I get a single .291" bushing, buy multiple neck bushings and segregate the brass by neck thickness, or turn the necks down for consistency, .014" and use the .291" bushing?

2) If I neck-size, don't I need a standard FL-die for new brass to be fire-formed?
( I think I answered my own question - buy a FL neck-bushing die and bump the shoulder back .002".)

Measure the case neck diameter of a completed round using the brass and projectile of your choosing.  Then buy the bushing that is 0.001" smaller...  or 0.002" smaller if you want 2 thousandth of neck tension...  If you change brass (even same brass, different lot#) or bullet, remeasure a loaded round to be sure of consistency.  As you get more experience, you will definitely develop "favorites" in terms of brass - all brass is not created equal!  

Accurately measuring neck wall thickness is not exactly simple as you may have noticed.

P.S.: You need to have a full length die (at least).  You can get them with neck bushings (Hornady and others).  You can also get a die with bushings that just does necks and not full length sizing.

Typically, the neck varies in thickness from about 0.013 as you note, up to 0.015 as you note, but BOTH MEASUREMENTS can come from the same case.
Thereby, If you want low consistent tension, the best route is to turn the necks to a consistent thickness.

And as the gentleman above noted, measuring case necks accurately needs something better than a dial caliper.

I set my neck tension with the expander ball or a mandrel. Unless you're neck turning your brass to uniform the neck thickness simply using a bushing die will not create uniform neck tension. Imperfections are pushed to the interior of the case neck when using that system and not expanding.

Virtually all brass will develop a donut at the neck/shoulder junction. This is made worse if you don't run something through the neck to push it outward.

I use custom neck full length dies to reduce working my brass any more than needed. I use expander balls (cheap and easily modified) to establish neck tension. I aim for .0025" to .003" of neck tension for any ammo that will be fed from a magazine. That includes bolt action rifles. I'll only experiment with less neck tension for long range ammo intended to be loaded into the chamber one at a time by hand.

I find that more neck tension usually works better than less. .001" of neck tension is not enough IMO. You'll need a bushing .002" smaller than your measured loaded round neck diameter and a expander ball .001" smaller than your bullet size to insure that imperfections get pushed to the exterior of the neck and any donut gets bumped out.

David Tubb, one of the top three or four best long range shooters in the country, has settled on .003" to .004" of neck tension for his match prepped long range brass. The USAMU is now using .004" of neck tension for their team ammo. Problems can be created if you use more neck tension than this, but this seems to be the upper end of neck tension that produces excellent results.

I am sold on Forster bench rest dies and I take advantage of their companies policy regarding modifications they will make to any die they sell. I send their full length dies back to them once purchased and have them custom hone the neck to achieve .003" to .004" of tension without an expander. I then polish some expanders to the desired neck tension. For instance I had a .223 die honed to .2445" and I have expanders that have been polished to .2205" and .2215". This allows me to push imperfections to the exterior of the case neck without inducing much or any opening of the case mouth.

I would suggest anyone sending their full length .223 dies to Forster to look at .243" as a good neck size. The .2445" I ordered is at the very limit (large size) of what will work for .223. .2435" will work well too. The same principle can be applied to any other cartridge.

Rule of thumb for bushings.

0.001" Tension for single loaded cartridges in bolt guns

0.002" Tension for magazine loaded cartridges in bolt guns that the rounds are run through the magazine

0.003" Tension for magazine loaded cartridges in semi auto magazine.

Another key to using them the brass have been fired in the gun it is going to be used.

I used Type S dies without the expander ball.  If I encounter a mangled neck, then I run the case over a K&M Expandiron mandrel.

Everyone has their voodoo!  

Dragging the expander ball through the case neck stretches it.  You can minimize with using a dry lube inside the case neck or using a carbide expander ball (Redding, (Lym Carbide makes a replacement assembly, and it also fits the RCBS FL Sizer)).

Consistency in you loading routine has more impact than you might think.

Some reloaders take off the high spots when neck turning.  Others go for a consistent neck wall thickness.