"...I've noticed so far with my gauge. Lee and Hornady makes just as good ammo as the more expensive Redding dies..."
It's astonishing how a good set of tools can get us passed all the BS about who makes the 'best' dies and presses, and case brands and .... whatever. On average, I find no consistant difference between any brand of conventional dies, or presses no matter how purty or costly some are!
For me, the best average necks have come from Lee's Collet Neck sizer dies, used along with a body die for 'FL' sizing. And the only seaters I think qualify for the label of 'competition' dies are those by Forster and Redding. And that wasn't
my opinion before I got a concentricity gage!
The 'best' way to measure runout is to position the gage at the point that shows the worst runout, don't try to find some mid point that reduces the gaged differences; that's only kidding ourselves. No matter how or where we measure it, the goal is to get runout to 'zero', not some present number. But we won't get there - consistantly - without tossing a lot of cases! Thus, each of us sets our own runout tolerance. Some of us do it by testing the results at the range; our targets tell us what our loads will do just as a concentricity gage tells us our runout. Seperate your loads into groups by levels of runout and see where your groups enlarge and by how much.
One thing to remember is actual runout is half of what the gage says.; TIR (total indicated runout) is the same error measured from two directions. Another thing is the max runout is limited by the chamber. Any chamber will force a badly bent round straighter, the amount of correction depends on how tight the leade fit is.
IMHO, the worst possible use of a concentricity gage is for bending the ammo straight. It can be done but the pressure can also damage thin jacketed bullets in the effort. The best use of a gage is to find where (and why) your runout is coming from so you can correct the cause. First check your sized cases; NO seater can make straight ammo in bent-neck cases.