Have also used a concentricity gauge to sort factory ammo, with very definite results. Once had a custom 7x57 with a Hart barrel and minimum chamber, and came across a very good deal on a bunch of Hornadys now-discontinued Light Magnum loads with the 139 boattail Spire Point. I sorted them into three batches, one with runout up to .003", another up to .005", and the third over .005". The .003" batch would consistently shoot into .5 or a little more, the .005" batch into around an inch, and the over-.005" batch into 1.5".
I've done a similar thing with 7.62x51 LC match ammunition in an accurate factory rifle. The results were strengthened by the fact the trigger man didn't know what he was testing, so no preconceived notions.
