Neck turning can be detrimental to brass life. It depends upon chamber clearance. If you have a factory chamber , then neck turning means you will need to stretch and compress the brass more aggressively after neck turning, which is worse.
This also leads into a conversation about the case manufacturer, because a turned Lapua case can be thicker than an un-turned Winchester case.
For neck turning to extend brass life you need to minimize the clearance between the neck and chamber, so to this point... what is your chamber neck diameter? Do you have your own chambering reamer?
Basically you are looking at the ideal chamber neck equal to bullet diameter plus turned brass thickness at the neck times 2 plus about 0.002"
Further to this, you need to give consideration to throat depth. You want to be sure that the throat allows the bullet of choice to be seated far enough out of the case that the shoulder at the boat tail is forward of the shoulder to neck junction on the case. If it is, then you will be clear of any donuts. If you are not familiar with donuts google the dreaded donut.
I double check my loaded round neck diameters to monitor for the development of donuts using a redding sizing bushing that is 0.001" smaller than the chamber neck. If that slides over a loaded round, its good. If it binds, then I need to turn the donut out.
The nice thing about neck turning is that it allows you to more closely control neck tension and as a result of that, control muzzle velocity.... at least isolate one variable.
As for the cases, I've grown impatient in recent years and just give a very light shoulder bump after every firing. I say impatient because the way I used to size was better... When I'm really trying to keep things tight, I start with FL resize and shoot once for practice. That produces a 1x fire formed case which is good for competition with neck resize only.
That creates a 2x fired case which for me is even better for competition... again with neck resize only.
I might get one more firing, depending on how hot the load is, but after that, I go back to an FL resize and the cycle repeats as above.
The nice thing about a tight neck is that you barely resize the neck and that means you cant induce runout between the case neck and body. The more you have to resize the neck, the more you will introduce runout, regardless of the dies you have.
I dial in my neck tension to within 0.0002" but that's because I have some custom made expander mandrels in 0.0002" increments.
Keep in mind that even with a tight neck chamber, resizing and firing does work harden the brass, just more slowly than a loose neck. To compensate for work hardening, you will need to use progressively smaller sizing bushings over time. So keep this in mind when ordering your sizing bushings.
Now in addition to better brass life, a tight neck with turned brass should better align the bullet as it starts into the rifling. This should (at least in theory) translate to an accuracy improvement. I think it does.
