Jmiverson
Do you have a neck thickness gauge? I have the one pictured below and it tells me me a great deal about my brass before I turn my necks with just on rotation of the case.
The reason I say this is turning the necks on poorly made brass will not make more it more accurate as pictured below.
If you neck turn the case above and only neck size your screwed and the bullet will not be aligned with the axis of the bore.
If you start with good quality brass with uniform body and neck thickness a neck turning tool "may" help. "BUT" with a standard off the shelf factory rifle neck turning "may" not show a improvement in accuracy and group size.
Also if you neck turn you only need to clean up 80% of the neck and take off the high spots "after" it has be fired the first time.
I disagree... When brass is fireformed, the OUTSIDE of the case expands to fill the dimensions of the chamber... ALL dimensions. As long as the chamber is cut properly and true to the bore, a fireformed case mimics the interior dimensions of the chamber so regardless of what may be INSIDE the case, the outside of that case fits and becomes properly aligned with that chamber.
The case is literally bent into shape.
Why most precision shooters will only compete with brass that has been fireformed.... and keep brass segregated for each chamber or use the same reamer for all related barrels
When you properly control the areas of sizing, you can maintain this alignment with the chamber. Remember, it is the back half of the case that does the alignment with the bore NOT the neck.
Outside neck turning is very important when using bushing neck sizing dies. Any variations in the neck thickness is "pushed" into the neck interior and that can cause issues with bullet seating. THIS is the main reason for outside neck turning... and of course proper clearance in the chamber.
Can you shoot superb accuracy with necks that vary a thou or 2 here and there? Absolutely.. been there, tested that.. BUT the neck sizing has to use another method.. ie Lee collet neck die.
I still outside neck turn every firing to ensure elasticity and clearance does not change... Brass can flow with every firing and that can really screw up your case neck dimensions unless they are controlled with every loading.
There is an argument that if you measure new brass and it varies in neck thickness, the case body may also vary.... more then likely correct (don't see the need to disect cases). The idea is that the powder column will not line up with the boreline and that can cause issues with ignition... BUNK.
When the powder is ignited, it tries quite energetically to expand tens of thousands of times in volume in nano seconds. That much volume of gas doesn't give a rip which way the case is lined up... it is going out the neck NOW.
Testing with cases that were severely out of whack in manf to prove this years back. The result, ZERO difference on target vs cases with concentric manf. What mattered was consistency in case volume and ductility of the case necks.
Proper annealing, outside neck turning and sizing... matters.
YMMV.
Jerry
