Originally Posted by dmax1800
1) why there can be more runout in the case neck than in the bullet; 2) which is the more important measurement, case neck or bullet runout for accuracy; and 3) if case neck runout is important, what can be done to correct it.
WOODS explained it well for a SAAMI (typical hunting) cartridge/chamber.
An unlucky friend had lugs badly lapped in a gun(unknown to him), and afterwards his go-to ammo started throwing shots all over the place. His ammo could show low runout(depending on gage), but the case heads were not square, as seen by rolling the cases across glass. After further work on the action and re-fireforming his ammo performed well again. I can only imagine his off-square case heads were setting a skew to cases chambered. And so I can imagine that crooked cases in general could cause throwing shots.
So I say the best we can do is make fully straight and square ammo, and use this in a precision fit chamber.
This is best seen with a v-block type gage, measuring TIR off necks AND bullet bearing.
But, with generous neck clearances and runout known to be neck thickness variance alone, a measure off bullets will suffice.