A couple months ago I decided to fireform new brass during a 1K BR match vs "wasting" the bullets, primer, and ammo to just fireform brass. The match consisted of three 10-shot groups, with each 10-shot group being immediately preceded by a sighter period.
As is often the case with new brass load round bullet runout was poor. Here were the results:
1st relay, runout of .004" or better - 7.81"
2nd relay, runout of .004 to .005 - 9.88"
3rd relay, runout of .005 to .006 - 10.5"
The wind was horrid that day and I wound up winning the match for aggregate, overall score, best single score, and I shot the smallest group.
It might seem that as the runout got worse the groups opened up, but we typcially have our groups open up as the relays progress due to the ever increasing wind, so I am not sure if it was wind or concentricity that caused my groups to open up.
I heard where several years ago the NRA said runout of greater than .004" made a difference for long range shooting, I think they were referring to 600 yds and beyond. Also, I have never seen conentricity make any difference at 100 yds.
Based on all that, I'll happily shoot a round in a 1000 yd BR match that has runout of .004".
I measure close to the case neck.
