Heres an interesting thought...
Bullets. Do the bullets themselves cause variations in ES SD. ??
Jacket density, or lead core density. What it one bullet is marginally harder or softer than the next ? One engraves easier in the rifling, altering velo and pressures ?
What if one has a longer driving surface than the next ?
Get a brand new bullet, roll it on paper a bit, and you get a duller surface, showing exactly how long the parallel drive band is. Do that to 10 bullets.. are they all identical length, or do they vary by 0.1mm ? Does that have an effect on engraving force, or engraving force duration ?
It gets to a point that variables are out of control, and we will never see a 25 shot string of 3 SD, 5 ES and a 0.3moa / 0.1mil group.
There.. i said it. Yes i expect to be wrong.. or right. No idea.
So here's a fun one I did recently. I sorted through roughly 1500 6mm bullets to finally get 30x of each on the high and low end of weight variation (about a 0.5gr total spread). And if you figure my average velocity in my 6mm ARC is ~2750 and that because the KE equation is 1/2mv^2 the mass term should be pretty linear and you do KE1 = KE2 (assuming the powder charge [chemical potential energy] being the same will result in the same final KE) with the two different masses (108.7 and 109.2, for example), you should see about 7-8fps change in the average of those weight sorted extremes.
30 shot strings:
108.7- 2735.6fps
109.2- 2735.2fps
ES within 3fps, SD well within 1 fps between the two.
So big picture takeaway, the transition of chemical potential energy into KE isn't 100% efficient, and there are many factors included as to what makes the peak pressure happen, the duration of pressure, and the sum of all of it that finally results in the muzzle exit velocity of a particular shot. At least in this test, the effect of weight variation is being grossly out-weighed by some other factor(s). Unfortunately I didn't think to measure base-to-ogive on these before I shot them but I still have a bunch of the rest of them I could go through and measure to see if there's any trend there.
At some point, however, things happen that are out of our control on a scale that's not feasible to control. At some point the scale to which a tuner "must need to be" to be "in tune" slips inside of variation of the forcing function we see from P&V results and that's where my level of skepticism about the whole thing comes from.
On aliasing...
The testing that Jayden did puts a pretty big damper on the whole "shoot 2, if they're not touching adjust the tuner...." until all 3 touch. We kind of suspected that going into it. The 3-shot strings do not correlate to the 20-50 shot strings (shocker). So maybe we aliased and skipped over the best settings, but what are the odds that we did it exactly 3-5 times per barrel to achieve pretty much the same results within the error brackets of what a 20-50 shot test will repeat to with/without/at different settings?
As someone else pointed out, to hit every setting with statistically confident results would take someone weeks of dedicated range use and several thousand rounds. To anyone saying we did it wrong, the world is just lying there waiting for you to do it better and share your results.
Again, I'm not saying that muzzle devices don't play a part in dispersion. I have been conducting a series of tests with this and in bolt guns, gas guns, the accuracy fixture I can document different levels of dispersion with different muzzle devices and that's repeatable. I just don't know that the reason why that happens if because of the weight/vibrations/mode shapes or muzzle exit gas flow, both, neither, something else.... Still digging into it.