Re: Get a GRIP! (on the bullet.... that is).
If you are using dies that don't have an expander (kind of unusual), then any variation in wall thickness (which you've already demonstrated is there (i.e. O.D. is the same, I.D. varies .0015") will cause uneven neck tension on the bullets. This will affect accuracy. Neck turning your brass will regularize the wall thickness, a good thing in a benchrest chamber, but really you need an expander to maintain a consistent I.D. A normal SAAMI spec chamber won't really notice small variations in the O.D. of your brass.
Life's too short to shoot an ugly gun.....