"This concept that taking a thousandth off will make a "sloppy neck chamber sloppier" is complete B.S. IMHO. A bullet has to leave the cartridge neck centered on the rifling and it will not do that if it is not released
concentrically around the neck of the cartridge. Neck turning does not center the bullet on the rifling (good brass prep and a good barrel does). Neck turning DOES ensure all the brass surrounding the bullet behaves the same way as it expands regardless of tight neck, no turn neck, or factory neck"
Note that I did NOT suggest that all factory barrels shoot poorly nor that all factory chambers are "bad", only that factory (SAAMI) chambers are NOT snugly fitted to factory cartridges, and that's a fact.
Given that there is, indeed, already a good bit of excess space in factory chambers (that's why we must at least neck size our cases to retain a new bullet isn't it?) is it not clear that any increase in that already "sloppy fit" is deteremental to cartridge fit? And does it not follow that a sloppy fit is detremental to accuracy? If you think that's not so, why would many people choose to order tight neck chambers in their custom rifles?
No one here but you suggested that cutting a thou off a neck is supposed to be excessive in any way. ??? Kindly note that I DID agree that "cleaning up" maybe 75% of an uneven neck's circumference can be a good idea, so did others. Our point is that going beyond a reasonable amount in neck turning is NOT helpful to accuracy. And a LOT of competent people agree with that. IMHO.
Those were my stated points. What's yours?