Runout

Can someone please define this for me. Thanks
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It is the amount usually expressed in thousandths of an inch in which a bullet's center-line is offset from the center-line of the brass cartridge case. There are handloading accessories made for the purpose of such a measurement. The more runout handloads have, the less accurate they are. I consider any runout of .002 or less to be of match quality.
 
^^^ This ^^^

Observable bullet tip "wobble" as the cartridge is rolled on a flat surface.

The more wobble, the more misaligned it is -- and the more it must try to
straighten itself out entering the bore in that critical first half inch or so.
 
The two before me explained it . The bullet should be perfectly centered, so when its chambered the bullet is centered in the bore.
 
It’s a measurement of how much off the axis of rotation or out of round an object is. A case, for instance, can be out of round and will have some runout. Or, a case may be perfectly round and the neck can be off center or out of round, in which cases the neck will have some runout. Or the case body and neck may both be perfectly round and concentric but the bullet can be out of round or not seated straight, in which cases the bullet will have some runout. A perfectly round and straight bullet will also reflect any runout in the neck. That is, if the bullet in a completed round shows runout, it may be because the neck isn’t concentric with the case while the bullet itself is just fine.
 
If the bullet does not enter the bore straight, the center of gravity will not be in the center of the bore. When the bullet escapes the bore, centrifugal force will fling the bullet off the center of the bore.

Mathematically and experimentally, this seems to cause ~ 2 moa error max on the target from 0.004" runout. The bullet can only be that far off, before the chamber bends the neck and bullet more into line.

That gauging bullet tilt article is for a loose SAAMI 30-06. Obviously some super tight 6mmPPC chamber would bend the ammo much straighter.
 
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