With hunting ammo, I do not like having my necks thinner then 14thou. Simply reduces the chances of neck splits or bullets slipping. This ammo has to work first and foremost.
With US commercial brass, there can be a slight variation in the thickness as you go around the circumferance of the neck. Is this a big deal? Not really but since we have the tools why not just tweak it.
By removing the high spots, the neck is of consistent thickness yet still thick enough to offer the higher neck tensions needed in mag fed ammo. Odds are you will find it hard to see any accuracy improvements on paper but it makes me sleep better.
Consistent neck thickness helps with consistent neck release which helps with bullets leaving straight so they enter the bore square with the rifling and fly straight to the target. Proper annealing is just as important as neck thickness.
ALL hunting chambers should have enough neck clearance in the throat so that a bullet will easily fall into the neck after firing. If not, removing some material from your case neck or enlarge your chamber. The last thing you want is for a bit of moisture to get on your ammo and cause a serious pressure problem by jamming up the case neck in the chamber.
I see a number of people building to BR clearances - actions and chambers - in a hunting rig. BAD IDEA!!!! Sooner or later, moisture or dirt will enter into the equation and there will be some serious problems.
We are optimizing the hunting rifle and ammo, NOT making a BR speced hunting rifle.
Jerry