"While I cannot provide proof, I can say to 'my satifaction' I believe that 'close to the lands, neck sizing, case consistency, carefully weighed, higher tolerance dies and free floated barrels contribute to better accuracy."
All of those things I listed can help, sometimes. It's the clear lack of "proof", or consistancy, that makes them myths, as I stated, "for best accuracy."
All of those points are often spouted as facts but they are NOT "facts"; they are no more than potentially helpful options that must be tested to confirm or discard on a case-by-case basis. Isolated findings by individuals are not facts for anyone but themselves. Repeating an occasional success story as fact without consistancy makes it a myth. I don't care what anyone says, or how out-landish it is on it's face, almost anything WILL work in an occasional instance or even in a large percentage of cases, but that doesn't make it a fact. The successful shooter may speak in authorative tones that something's true (for him) but, as a flat statement, saying anything WILL aid accuracy is NOT justified unless it is true in a large majority of instances.
So, it's certainly valid to say this or that may help, but saying it will help is a whole 'nother thing. Neck sizing helps ... sometimes. Floated barrels help ... sometimes. Seating in the lands help ... sometimes. But individual conditions change things.
Weighing charges may help... but only IF the load is on the ragged edge of what will produce top accuracy. And that optimum charge IS a range, not a single specific point, plus or minus nothing. Etc.
I do a lot of trivial "precision reloading" stuff because I enjoy doing it and I feel good about dong it but I know much of it has little or nothing to do with fine accuracy and I don't propose it as true for others. No matter what I THINK, or what has actually worked for ME, if it isn't provable and repeatable for others then it's only a potentially helpful option, not a rule anyone else can depend on. A myth.
I will take time to address two specific points from the above disagreements.
I defy anyone to "prove" the statements about "tighter die tolerances" (whatever that means, anyway) can be found in any brand of dies. Dies are machine made and they have a SAAMI tolerance ranges, max diameter/length, vs. minimum and all our makers seem to stick to them. Anything falling within that range is fully "in tolerace".
So, I must ask my friendly dissenters, "On what side does a "tight tolerance" die go towards?" Is it the Max (largest die chamber, cut with a new reamer)? Or Min (smallest die chamber, cut with a worn and reshapened reamer)? And, if it's assumed to be the smaller side of the tolerance range, how does that help with a rifle chamber that is cut on the larger side of a simular range of tolerances? (Everyone should know there is no overlap between die chambers and firearms chambers. By SAAMI design, the largest die chamber is smaller than the tightest gun chamber.) So, consider those questions and you will soon understand that the claim of "tight die tolerances" without including the firearm's chamber/fit, actually means nothing! Meaning, the value of "tight tolerance dies", as such, is a myth.
Now, Hornady's sliding bullet seating chamber does ONE thing well; It makes sitting a bullet on top of a case easier. The loosely fitted floating sleeve does nothing to align the whole case (as Forster and Redding's full chamber, spring loaded, sleeves do). The floating sleeve's inner fit to the bullet itself tends to be oversize - sloppy - as is its free-sliding fit within the die body. Without some way to center the lower portion of a case, the limiting factor of the seating die's total alignment system becomes the press's elevated ram/shell holder, and that ain't precise! Therefore, good bullet alignment with that die is as much pure chance as any other conventional seating die.
Basically, Hornady's floating bullet sleeve design is no more than a slightly modified copy of a method that goes back to at least the early 60s. It was tried back then by several other companies, including Lyman, Vickerman and Herters, but got dropped because it added cost without any average gain in cartridge concentricity. Still doesn't. So, Hornady's sleeve seater is good but being "better", on average, is a myth. And that's provable.
Some myths seem so clearly true and are so deeply engrained in our minds that they seem to have a life of their own!