I've been reloading for a decade now and I've always heard you want to keep case lube OUT of cases. I just swapped out my Redding FL .270 dies for another quality brand of precision bushing dies and noticed up to 0.010" variation in base-to-ogive length between rounds. I called the die manufacturer and they told me that wet tumbling with TurtleWax Zip Wax will put a very thin layer of wax inside the neck and seal the pores in the brass, making seating more consistent.

My reaction was one of skepticism, telling him that I had always been told to not get any lube near the powder, but he told me that recommendation came straight from a guy who makes a living manufacturing match ammunition for competitive shooters who do not want to make their own ammo.

Does anyone else have any input on this or am I going to have to just try it and see for myself?

You're thinking wet case sizing lube.

It's general practice to lube moly-coated bullets with carnauba wax.  Doesn't hurt nekkid bullets, either.

I haves used liquid wax from garage sales as a media activator for Decades
No adverse effect noticed by me!

Nekkid bullets?!

But seriously what do you mean by "wet case lube"?  My general practice is to decap the brass with a universal decapping, wet tumble with dawn/lemishine/SS Media, lube with lanolin-based case lube, tumble the lube off in the wet tumbler, then primer, charge, and seat.

I used to use Lee Case Lube and when it dries it is not an issue.

You just do not want "tacky" lube left in the case sen it would attract powder and potentially contaminate when instilling powder

My thoughts exactly, which is why I'm meticulous with removing the lanolin based lube.

The turtle wax zip wax is a liquid soap with wax embedded in it.  It's not a case lube and it's not going to effect the powder or make the cases sticky. When Dry tumbling in corn cob it's common practice to add brass polish which is mostly wax with other stuff mixed in. Ive used turtle wax zip wax while wet tumbling and it works just fine. It's used to try and replicate the thin layer of wax left on the brass you would typically get from dry tumbling with brass polish.

You are doing something wrong.  You should not need to wax inside the necks to do much better than this.

How variable is the headspace on the sized cases?

How variable are the bullet lengths (base to ogive)?

Are all bullets from a single manufacturing lot?

What bullet seater are you using?

Just for grins, check that your dies are clean and tightly mounted in the press.

I have heard of people complaining that their brass is "too" clean after using ultra-sonic cleaners or steel pins/dawn/lemonshine. The residual carbon deposits in the neck that are left over after the "old fashioned" tumble cleaning actually acts as a lubricant when seating bullets.

I think you're worried to much over nothing. All bullets are tough enough to be seated in a pristinely cleaned case neck without causing any harm. Over all length on my match ammo routinely varies +/- .008". The bullet tips have irregularities which causes this variance. It hurts nothing as far as accuracy is concerned.

I think the headache of trying to apply lube to the interior of your case necks prior to seating bullets will create more trouble than it's worth.

I'm using a Whidden seating die. I'm measuring from the case base to the ogive of the bullet, not the tip. These were sized on a Mec Marksman with a Redding FL sizing die set for a slight cam-over.

When I first began loading on a single stage, I would use Lee lube on a wire brush to lube the inside of necks so they wouldn't drag too hard on the expander button.

You did not mention taking any steps to address differences in shape bullet to bullet.

Bullet seaters do not push down on the bullet tip, nor do they push down on the point on the ogive you measure to. They push down on an unknown point between the two, and the distance from there to your ogive measuring point can and will vary bullet to bullet.

Should you choose to deal with this variation, IMO the best way is by seating long, measuring CBTO, and then adjusting your micrometer seating die so that the second seating results in your target CBTO measurement. In that way all cartridges will have the same distance from bullet ogive to the lands . . . which presumably is the reason you're measuring CBTO in the first place.

Others may advocate sorting bullets by ogive length or bearing surface length, but IMO neither of those deals with the fact that this particular source of variation occurs between the bullet's ogive (ie measurement point) and tip.

Hmmm that's a good point, TwoBoxer.