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Bart B. you mentioned how Sierra had not found a issue but did you have all the details?
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I think I do. What are all the details you want to know?
They first came from the two people who worked in their plant reloading and testing all the ammo used testing their stuff for accuracy. I've shot many a match with the first one. And I've walked through their plant and observed all the stuff they do and use.
Sierra's been using unprepped cases testing their bullets for accuracy for decades. Perhaps the fact that they full length size all their cases in over-the-counter dies, use rail guns (which eliminates virtually all the other rifle and human variables effecting accuracy) with match grade barrels with virtual SAAMI spec chambers (not "tight" so-called match chambers), shoot in indoor ranges and don't work up new loads when changing any component lot. . . .has no bearing on the primer flash hole issue. All of which is their fancy equipment and details. It's no different that what benchresters use.
Sierra's tests are typically 10-shot groups fired with bullets grabbed as they come out of the final jacket forming dies (at 80 to 90 per minute). They're seated in sized and primed cases with metered (not weighed) powder charges. Then all 10 shot in the rail gun in a couple of minutes, measured, logged then 10 more are taken and shot. Several dozen test groups are shot during the production run of a given lot. I've seen a set of groups shot in the late '60's with their .308 168-gr. match bullets and all well under 1/4 inch/MOA with an average of just over 1/8 inch. The curent IBS benchrest aggregate record for five 10-shot groups at 100 yards is .1898 inch/MOA average and was shot with totally prepped cases including flash holes.
Complete match rifles have been tested with unprepped flash holes in the cases that shoot under 1/4 MOA at 600 yards and 1/2 MOA at 1000 yards; group after group after group. One tested some years ago (with unprepped flash holes) shot several 10-shot groups at 600 yards; all were under 1.5 inches. The NBRSA 600-yard aggregate records for six 5- or 10-shot groups are in the 2 to 3 inch range shot with totally prepped case flash holes..
I well understand the premise that uniforming every single element and detail of a cartridge will make it shoot bullets more consistantly. But when one gets down to those that make a low, single-digit percent change, can you shoot your stuff accurate enough to reveal it? On the other hand, seeing something "perfect" in your components does make one feel good. And nobody shoots well if they don't feel good.