I have tried several things as neck turning lubricants. With a carbide mandrel, they all worked. The main difference between them is the ease of getting them off of the brass. RCBS Case Lube II is a clear, water soluble sizing lube that also works for turning necks, and dissolves in water, the safest solvent of all.
One other detail that is worth mentioning is that when fire forming PPCs with pistol powder and NO BULLET there is a little powder fouling left in case necks that actually helps prevent metal transfer to turning mandrels. Of course this is more of an issue with steel mandrels. I only brush the inside of necks lightly after fire forming, leaving a light and, what appears to be, uniform dusting of powder fouling in the necks. This forms a bit of a slurry with the lubricant that is similar to the particulates in anti-seize compounds.
This also comes into play when fire forming by shooting .22 bullets in a 6PPC barrel. I rough turn to .010 with a relatively loose fitting mandrel before the sub caliber firing, and then lightly brush before expanding and turning to final thickness at 6mm. For those that may be concerned that the brass thickness may be off a ten thousandth because of the fouling, you should consider that it will always be there, because I never clean it all out of the inside of the necks, and one firing leaves a relatively uniform deposit in all the cases ( I hope.).