Pardon my ignorance, but.....................

[Dusty Miller]

What the heck is "run out"?  I've done very little rifle reloading and this phrase is a mystery to me.

[John Traveler1]

runout is a machinist's term for eccentricity perpendicular to a rotating axis.

In short, visualize a loaded cartridge held and spun on it's long axis in a precision fixture.  A dial indicator measuring tool is used to measure how much it is out of "perfect" rotation from that axis.  That measurement is runout.

These measurements are important to the precision shooter (competition, varmint, long-range, etc) in getting perfect ammunition.

HTH
John

[longwinters]

I always thought of it the same way that an archer cks his arrows for straightness.  I put my arrows on an arrow straightner and then the gauge tells me if there are imperfections in straightness and if they are within tolerance.  But when spinning the arrow on the wheels of the straightner I can also ck the arrow tip for wobble etc...  Of course the more wobble the more problem the arrow will have to shoot straight.

Long