On inner case necks, they should never be squeaky clean. Certain tumbling methods and cleaners are particularly bad in that respect.
On fired cases, the powder residue left in the case neck is all they need for seating. If you feel like you have to do something, a quick pass with a nylon brush and you're done.
For lubing the inner necks for sizing when using an expander... lots of stuff works well. You want to reduce the friction as much as possible so the expander doesn't pull the neck out of alignment with case as it passes up through the neck and expands it.
With a standard F.L or N.S. die, the best approach is to not excessively reduce the neck diameter in the first place.
Good shootin' -Al
Al, that's been my experience as well.
Some more general comments on this thread:
Have found that bullet run-out matters far more in some circumstances than others. In my 6mm PPC benchrest rifle I've found run-out of more than .001 results in 5-shot groups at 100-200 yards doubling in diameter, but that's with bullets with flat bases (or very minimal boattails), which tend to result in more consistent gas blow-by at the muzzle than "full boattail" bullets--which is of course why short-range bench shooters tend to use flat-based bullets.
Boattails tend to de-stabilize slightly at the muzzle due to powder gas blasting along the rear half of the bullet. But at ranges longer than about 250-300 yards, boattails tend to group better, despite often not tending to group as well at 100-200 yards, because they resist wind-drift better--which is also why bullet run-out isn't as critical at longer ranges. (The effects of wind on group size also grow larger, one reason many hunters think bullets tend to de-stabilize at longer as their velocity drops--when bullets actually become more stable, unless of course they approach subsonic velocities.)
When I acquired my first bullet-runout gauge over 30 years ago, an RCBS Casemaster, the directions suggested that .005 bullet run-out got about as much accuracy as possible out of typical big game rifles, and .003 in varmint rifles. I found this to be generally true, but also depends on the quality of the rifle, brass, bullets, loading techniques--and of course the shooter.
