Among the various .22LR cartridge components, weight differences between rounds is most likely associated with bullet mass being different. Bullet weight makes up about 78% of a .22LR cartridge's mass. And higher grades of match ammo should be expected to have bullets close in weight.
For the general reader, according to in George Frost, Ammunition Making, weight variation for .22LR bullets should be kept within .2 grains for non-match bullets, within .1 grains for match. (p. 29.) In his chapter on .22LR match ammo, Frost says weight control in bullet manufacturing should be within a range of plus/minus .05 gr. on any sample of ten bullets. (see p. 135.)
It's common sense that with all else between cartridges being equal -- that is the amount of primer/propellant, crimping -- heavier bullets will have a slower MV. Rounds with a slower MV can be expected to have a lower POI than faster ones. The exact weight of the bullet shot always remains unknown to the shooter.
I don't know what ammo he was weighing, but nothing I've weighed had bullets that varied so little. The brick of Eley Club that I measured the other day looks like this:
I've measured a lot (many 5000-round cases) of ammo, and I've never seen anything with bullet weight variance as low as that guy's talking about, so I am afraid I call BS on that one. I have three muffin tins that I use for sorting, and they're half a dozen bins each, and are labelled in 0.1-grain increments. It is unusual if I have more than a handful that don't fit in those 18 bins, as was the case with this lot of Eley Club. It needed 20 bins, but barely. Most of the time those 18 bins are enough, and a small number of them are likely to go unused. Never have I ever measured a brick or case of ammo and only used 2-4 bins, which would be the case if I saw similar results to that dude. Usually ~15 bins is enough, and it doesn't go over 18 often.
It's possible that identical bullets with the same MV can be the product of faster primer/slower powder or slower primer/faster powder. The problem is that no one can know if -- or when -- this may be the case. There's no way for a shooter to identify and confirm or even measure different "acceleration curves" . He can only know the MV of the bullet.
Regardless of how these bullets arrive at the muzzle, they still have the same MV. Within the length of a barrel, say 24" - 26" or so, there's not a lot of room for variation concerning how two bullets arrive at the muzzle with the same velocity. In other words, since bullets don't accelerate after leaving the barrel, bullets with the same MV should have similar acceleration curves in order to get from a standstill in the chamber/leade out to the muzzle.
To return to the previous point, barrel vibration patterns are either always random and independent of MV -- or they are always related to MV. They can't be both at the same time. If it's the former, accuracy performance and consistency is all the more challenging.
The question remains, why some rounds have MV/POI match and some have MV/POI mismatch.
You don't need to know whether or not their acceleration curves were different. You only need to understand that it is possible to have different acceleration curves and still arrive at the same muzzle velocity. But you do not seem to be able to fathom that this is possible for some reason. Just like it is possible for two different cars to both cross the finish line in a 1/4-mile drag race at 150 mph but have very different elapsed times it is also possible for two bullets to have the same muzzle velocity but take different amounts of time to exit the muzzle. You still don't seem to be understanding barrel harmonics properly with this statement. Barrel vibration patterns aren't random. They're actually fairly consistent. What's not very consistent is when bullets exit the muzzle in relation to their vibration pattern. When your bullets are leaving the muzzle at different times despite having similar muzzle velocity values the reason their POI differs is because of different exit times. And BC differences also contribute. The latter being one of the reasons even a well-tuned rifle doesn't make super tiny ragged holes 100% of the time. Muzzle exit times differ. And bullets differ. We can only do so much to mitigate all the varying factors. And thus, POI isn't always what we think it should be. The more control we have over everything, the more sense the POI will make.
Just because the mv’s can be the same, it does not represent how it got there. I am sure barrel vibration would be different, and has the potential to change poi. In centerfire, two different powders with the same velocity and the same components are not likely to have the same poi. I don’t think rimfire can be made perfect enough to have common mv as the only contributing factor to poi shift.
As I understand it, barrel vibrations are pretty similar no matter the ammo, as they're largely dictated by the physical characteristics of the gun and everything attached to it. The magnitudes of what is going on can differ depending on the ammo, but the overall behaviour stays mostly the same. Different primers and powders affect muzzle exit time, so we see the same effects there resulting in different POI. How much energy there is in a given round can affect the magnitude of what goes on, but the what goes on part is more or less dictated by the physical characteristics of the gun. Barrel contour and length, mass of the gun overall and its centre of gravity, these are things that determine what that barrel is going to do during firing. There's even
at least one calculator available on the internet that can show you what the basic behaviour of the barrel will be based on those things, including the overall mass of the rifle and how far above/below the bore the CoG is, which will be affected by the scope and stock, etc. And in case you miss it while glancing at the calculator, it is entirely missing anything to do with your ammo or load because it doesn't really matter here. And I think that's precisely because the ammo only changes the magnitude of what's going on. The variables you can enter into that calculator are what's responsible for the general behaviour, not the load.