Honestly speaking, this is out of plain curiousity. For my current barrel, I have two loads that shoot 1/3 MOA at 100-300 yards, that I've tested multiple days. I'm fine where I am at, I'm just curious as to what makes these things accurate and precise
Just a few random thoughts while I am stuck waiting... skip to the last paragraph for the punch line...
Many of us on the forum have been reloading at home for decades. Many times folks start out and get lucky, other times they struggle up front. Far too many give up too soon.
I was the first type, or at least I think I was... My very first attempts at rifle hand loads though a factory Rem 700 30-06 were so much better than factory ammo that I was fat dumb and happy for a while.
That was northwest Indiana in the 60's and 70's where there was no highpower hunting season for the most part. We only had shotgun and archery for deer, so highpower was only for occasional woodchucks or predator controls.
I thought in terms of farm work that my 3/4 MOA was pretty good considering most shots were under 300 yards. We didn't have rangefinders. We counted fence posts or corn rows..... What did I know? I shot with peep sights and holdover after doing load testing with a K-Mart scope. I wasn't exposed to HP competition or benchrest at that time and place. I was vaguely aware of what accuracy could be through reading magazines at the barbershop since I couldn't afford them and nobody around had the interest.
Fast forward to being recruited at 19 years old into an advanced defense company and I found out that what I thought was great was just so-so in other circles. It was then I learned that those early results would be temporary and sometimes hard to repeat without serious effort. (I'm mostly describing brass prep at this point.)
I learned what state of the art really meant and that my early success at 3/4 MOA was good, but the next batch of brass wasn't the same result.
It took me into the early 80's to sort out for myself what was important and what wasn't, but I also had world class experts as mentors so I probably got there much faster by their advice. Keep in mind by now I was building and running labs and doing advanced weapons systems development for a living. However, Uncle Sam may load by the millions, but he he has zero interest in reloading....
Things at work taught me a lot, but at home I was subject to my own pocketbook. At that time we had Bower's Wholesale in downtown LA and the Sierra Bullet factory was local and also very kind to young competitors.
While picking silhouette as the cheapest way to stay tuned up for elk seasons, I learned that keeping things under control at 600 yards wasn't going to be as easy as I first thought. I could get bullets cheap, and had easy access to powder and primers without much effort, but match quality brass was the same for all of us, difficult.
One could get mil-surp and commercial easy enough, but we are discussing state of the art match accuracy as it relates to today's brass. Uncle Sam was giving me as much used brass as I wanted but boy was it work to turn it into acceptable. Occasionally we could get virgin LC or "special" commercial brass, but it still wouldn't make you happy. It took tons of sorting and prep work.
We are far better off in terms of being able to purchase batches with tight quality controls than we have ever been. In today's world, we can go no-turn and no-sort and in most cases be competitive (depending on your context). That said...
The whole point of that story is the previous generation had typically been forced to learn the answers to the question of what matters in brass prep and what doesn't. That was by necessity.
I learned the hard way by getting burned. Some batches of brass were really bad, and others were really good. That experience taught me to test the question at hand, which is "when does the weight of a piece of brass from a batch create a flyer on the target or cause me to re-tune?"
For now, I don't sort, turn, or do any extraordinary prep for <600 because I sample screen fresh batches of brass. That is mostly Lapua to be specific and the reason is their QC is good enough for Midrange or Service Rifle. That hasn't been true of many other brands, in the past or even now. I can see the difference at 1000 so I admit to some more screens for those.
So I would suggest two things, one is to spend some time early in your life learning to sort/screen your components to learn what their typical stats are running. Learn to save the ones that are "off the tails of the curve" and store them till you can run tests. That may not come from one batch, but keep watching cause sooner or later there will be an escape.
By getting your own experience you will learn what that brand is typically giving you, and when it becomes a reject. The exact value isn't the same for every caliber or context. That doesn't mean you can't ask around within your area of interest, but that is trying to say that what works for F-Class may not work for Benchrest, the value for a 338 is different than the value for a 223, etc.
You will be far better off doing the work yourself over time than just taking my word for it. The motivation will come as a matter of time. Sooner or later, material shortages, tooling changes, brand substitutions, etc., will burn you on the target and you will want to know what just hit you... YMMV