I want to share my reloading routine which I developed with a .338 win mag that would not shoot as well as I wanted, with the bullets I wanted it to.
It's shooting just fine now, but I came across a new issue.
The two things I wanted to address are neck tension and concentricity.
Neck tension became an issue when I thought it was the reason why I wasn't able to get consistent seating depths and bullets being retained in the die.
Turns out it was a die issue. Concentricity, well, because. I don't measure it, but we all want more of it.

I give my cases a wipe down with a rag to get the soot off, slip on a latex glove lube up with imperial die wax, then give them a spray with a silicone lubricant.
They get run through a collet belted mag die, which is something I've never had to do in reloading over a dozen belted mags for 15 years. This operation is a real pain, and I am contemplating getting some custom dies for this rifle, which must have a chamber on the large side of the specs.
Then I run them through a Forster FL die.
According to the instructions with the collet body die, it should be done the other way around, but these cases will not run through the FL die unless you resize with the collet first. If you force them through, it shaves brass off the bottom and they are prone to sticking in the die.
Then I tumble in stainless media and dry.
After that they get run through the FL die again, this time with no expander plug, which by the way I always polish in the lathe.
Prime, charge.
I seat in two increments, by running each case through the die on a "zero" setting then a second time at the final depth. Second time is bump of 1mm (0.04") and I also turn the cases and give them a second gentle bump at the same setting.
Now, what I don't like is that I noticed that some cases shave copper off the bullets and some don't. The bullets are CNC turned and there is no inconsistency in diameter, so it must be the case necks.
Is it due to the tumbling and drying or the second pass with no expanded that does this? I’ve noticed it happened more on this firing than the first. It is Nosler custom brass, so there was no need to chamfer the case mouths, but it would have been a good idea for the second firing.
The accuracy is good, half MOA, but I have to check now that the cartridges that shaved shoot the same as the ones that don't shave.
Anyone else have this happen?

If I follow your process, you are loading the bullets into case necks which have been reduced in size by the FL die, but not re-expanded by the expander ball. This would mean that they are several one-thousandths less than the size of the bullets, thus as the bullet is seated you get (at least occasionally) shaving of the bullet as it is seated.

It's not clear to me why you run them through the FL die a second time. There should be no need for this, and it amounts to working the brass unnecessarily and results in under-sized case mouths.

Right.
You need to chamfer your brass, this cannot be skipped, and use the right size expander ball.
And all that sizing up and down will wear out your brass, I recommend you polish your die out until it works.

I am running them through the die twice, the second time with no expander plug.
Reason for that is that the I shoot are CEB's and they are undersized by .007 so by doing this I get back up to a better neck tension.

The necks of the cases probably have enough variation in thickness such that the outer diameters are the same due to the second pass through the sizer but the inner diameters vary because the expander ball is removed.

You could skim cut the outside diameter after sizing with the expander ball in place to true them all up.

I had thought about giving them a skim with the neck turner, which should also bring the neck tension down to around .005".

When I said use the right size expander plug, I meant, for your bullets. Just because your bullets are .007 undersized does not mean you can get away without any expander plug at all. What is the ID of the brass, sized?