One thing people tend to do when turning necks, is to make them fit the chamber necks more closely than factory brass of that size is. Tighter fitting necks, of course, means the turning tolerances must be tighter as well. I was referring to inside reaming to turn the brass into factory spec. neck thickness for that round, which would be on the order of .010" to .012" thickness.
; Runout is more often caused by dies bending the brass during sizing, rather than by neck thickening.
; The time to check brass runnout on the outside of the necks and case neck thickness with a ball mic is just after firing. That will tell you if the necks are out of sync and therefore runnout is bad as a result. I've done a lot of case forming and not had trouble with thickening necks.
; .358 Winchster brass is easily made from .308, 7mm/08, .260 Rem. and .243 brass, without needing to turn or ream, ever. It's cheap enough that $50.00 or $60.00 worth will last a lifetime, well, almost, when you include range pick-ups.