What Lefty said. The basic all too elusive one hole group of 10 shots at 100 yards or more is theoretically possible if everything, and I mean everything, is exactly the same shot after shot after shot after shot, etc. Those who pursue this goal spend a great deal of time and effort in trying to make sure the volume inside each case is the same, the primers blow the same amount of flame, the powder is exactly the same, the bullets are exactly alike and seated to the exact same depth, and so on. I used to shoot with one guy who used a runout gauge to find and then mark the high spot on his rounds. I think he would have spun balanced them if he could have found a little machine to do that, too. He had a self made solid aluminum stock with a 40XB action, 2 ounce trigger, ultra heavy barrel and all the other tricks that were around 35 years ago. His rounds looked like jewels because he polished them - not just cleaned, polished.
He still didn't shoot a whole lot better than everyone else, but he had fun trying.
Uniform flash holes certainly don't do any harm, but how serious are you about the rest of your case prep routine? Do you weight sort them? Group by length, headstamp, age, number of firings? Measure neck thickness? Inside and/or outside turn the necks? Check finished rounds for concentricity? Use match bullets? Match primers?
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