One old-time champion benchrester characterized all of this in terms of "identity" (his characterization of the highest level of consistency). In theory, if you restrict your thinking to the ammo only (everything from the rifle to the environment to the shooter also affects both precision and accuracy), if you were actually able fire the SAME cartridge over and over again (obviously fantasy), the round SHOULD perform exactly the same way each time. So, the goal is to make every cartridge EXACTLY the same as every other.The parts of the process I still fail to fully understand a need for are neck turning and annealing. I used this article for the reference so far:
You are being redirected...
www.accurateshooter.com
The neck turning step - is it supposed to be done before neck sizing die? Does new or 1-2 times shot brass really need it?
Case weights/lengths/volumes/etc. are all approaches to be able to sort brass so you load cartridges that are identical to each other (in the limit). None of these actually achieve "identity" as even small changes in case dimensions affect pressure gradients/flash vortices/burn kinetics/etc. which COULD change when the bullet leaves the case and the dynamics of that departure.
The two techniques you mention (neck turning and annealing) get used to make the cases "more similar" to each other. There are variations in wall thicknesses between cases and at different points around a single case. Variations may lead to less case deformation at one point of the neck than another during firing, and they COULD affect consistency of how the bullet is released at different points around the case neck. Turning removes thicker parts of the neck so that the brass is the same thickness all the way around the area holding the bullet.
Working the brass causes "hardening" of the metal, which also changes the holding/release characteristics of the neck on the bullet. The process of annealing is intended to return the hardened brass to it's initial, softer state. Ideally, every case will have brass of the same thickness/length/dimensions/hardness/etc. so that every case acts as if it is identical to every other one.
Turning is usually only done once (just like flash hole uniforming). The case neck needs to be concentric in order for the turning blade to leave the neck "perfectly" circular, so sizing and mandrel expanding to make the inside of the case neck "perfectly" circular is generally considered to be the starting point. Then, the turning blade running around the outside of the case neck carves off the high points until the brass is all the same thickness.
Every time you fire and size the case you're introducing changes to the shape/thickness/physicial characteristics of the brass. I don't think "rabbit hole" even begins to describe how crazy this gets. The amount of time/effort/money you invest in making your handloads "identical" is probably dependent only on how rich and how nuts you are, and how precise you actually need your ammo to be. If the precision is your hobby, have at it. If "good enough" is good enough, just decide early on which parts of the insanity you're just not willing to endure.