...are you saying that you slip a nylon washer over the neck and onto the shoulder of your rounds to be measured? If so, an accurate runout measurement would then depend on the concentricity of the washer, right? I'm testing runout on a Sinclair runout tester with two ball bearing 'roller points' for lack of a better word, with the runout mic riding on the bullet's surface, about half way between the case mouth and the bullet point. Is this your procedure as well as to the measurement point?
My questions are for both of you, Unclenick and Bart
...here's my setup...am I doing this correctly? On good .222 Magnum rounds, bullets seated in a Redding Micrometer die, I get .000 to .004" runout as depicted in the pic below. Case runout, with factory new, unfired cases, before sizing or seating, measures .001-.003 at a point midway between the case mouth and the beginning of the shoulder; resizing in a new RCBS FL sizer plus bullet seating add's another .0015" or so to the overall measurement.
I also use a Lyman "M" die to expand case mouths prior to bullet seating. I do not tighten this die down in the press, having better luck allowing it to 'self-center' as the expander mandrel enters the case mouth. A somewhat limited amt of testing with this procedure seems to indicate that groups are improved, tho it's hard to tell if the runout is any better.
I should add that the rifle is capable of 3/4" gps at 100 yds for 7 to 10 continuous shot strings, with some cooling between shots...(depends too on how good my eyes are working on any given day!)
One last question/observation....is runout as we're discussing it, of material benefit in a light wt. bolt hunting rifle (less than 8 lbs with scope and sling) at 250 yds or less? I do know that my AR in 5.56 (Colt Match Tgt HB) does better at 600 with hand selected cases, Sierra 80 grainers, and minimal runout.
Best Regards, Rod