... if you aren't using brass that has been meticulously prepped and sorted and checked for runout, all this oal business could be for naught.
Rounds that are not concentric with the same internal volume and/or have a sloppy fit in the chamber will be all over the paper no matter how great the powder charge or how far they are off the rifling.
This flies in the face of military semiauto match rifles with huge mil spec chambers shooting commercial .308 Win. match ammo with minimum case dimensions staying inside 4 inches at 600 yards all day long. And do so starting out with .020" jump to rifling in a new barrel to .100" at 3000 to 4000 rounds later when the barrel's worn enough to notice accuracy falling off.
And Sierra Bullets' first Ballistic Tech who tested virtually all their bullets for accuracy in super match grade barrels fitted to rail guns with chambers at or virtually equal to SAAMI specs claimed: "the round has to fit the chamber like a -CENSORED--CENSORED--CENSORED--CENSORED- in a punch bowl." He (as well as so many other top high power match rifle competitors) felt and still feel the same way. Sloppy fit of case to chamber diameter wise is ok but headspace clearance range has to be a small spread. For rimless bottleneck cases, one with a sloppy fit diameter wise will align the bullet just as well centered on the bore when fired as one with a tight or minumum clearance case fit will.