It sounds like you're neck turning for a factory rifle, which in my experience is mostly a waste of time. If the case necks are turned enough to make them uniform they usually end up too small for the factory chamber neck. That means that every time they're fired the necks will expand more, and have to be reduced in OD more to hold a bullet again. That leads to premature work hardening of the necks which leads to premature neck cracks/splits.
If the cases are bad enough to need turning they're likely bad enough that turning won't improve accuracy that much if at all.
Measure the neck thickness with a tubing micrometer at 4 to 6 places around the neck, or use one of the rigs sold by Sinclair Int'l and others that uses a dial indicator to measure the thickness of the necks. Any that are more than 0.001" to 0.0015" different in thickness - usually one side with be thick and the opposite thin - should be discarded or used for something where topnotch accuracy doesn't matter.
But, if you really want to neck turn, what I do is:
1. Run them through a neck sizing die to round the necks up and remove any dents or dings. They can be FL sized too, but it's not necessary at this stage.
2. Run them over the expander using Imperial Sizing Die Wax or another sizing lube on the inside of the necks to make the job easier on you and the case necks.
3. Turn the necks, adjusting the cutter to give the thickness you want. You indicate that you're not turning to any particular neck thickness, but you're going to have to measure the neck thickness in order to not remove too much brass for the reasons stated above.
It's necessary to lube the cutter pilot with a little dab of some kind of lube, Imperial Wax, or some other lube or the pilot will heat the case necks, the necks will gall leaving brass on the pilot, and it gets worse from there. If you remove the shellholder from the K&M handle it fits in a cordless power screwdriver and is easier and does a better job than turning the case by hand.
4. Resize the necks. If the necks are turned too thin it will be necessary to use a sizing die with neck bushings to get the necks sized small enough. Necks that are too thin are less sturdy than thicker necks which can be a consideration in ammunition that will be fed from a rifle's magazine.
