What is neck turning?

[AllMovingParts]

While reading through the case prep sticky I read a post that mentioned the importance of neck turning in addition to case trimming. I am just starting to reload .223/5.56 and am not familiar with steps used on necked cases that are not performed on pistol cases.

[GEmanuel]

Neck turning is where a cutter removes brass from the inside and outside of the case neck/mouth. Primarily to insure concentricity and consistent tension on the bullet as it is held in the case.
You mention .223/5.56. If you are in fact using a .223 in a bench rest rifle type scenario, you may gain some benefit from performing this extra step.
If on the otherhand, as you also mention 5.56mm (usually used in concert with an AR platform) neck turning is a total waste of time as the rifle itself is not precise enough to realize the benefit of neck turning.
Trimming on the otherhand must sooner or later be done on all necked cases as they tend to grow a little with each firing/sizing cycle.
One last caveat, do not fire 5.56 in a rifle that is chambered for .223 using military ammo. The pressures are much higher than the .223 chamber is designed for. You can however fire .223 all day long in a rifle chambered for 5.56. As you are reloading, if you are in fact loading for a .223, feel free to use 5.56 brass using the .223 data from a good loading manual. Just make sure you work up your load looking for signs of excess pressure.
There may be other consideraions, but, this should answer your basic question.
Hope it helps.

[AllMovingParts]

I will be shooting in an ar15 designed for 5.56. The post mentioned the neck turning being needed to prevent the material from becoming too thick and pinching the bullet, causing higher pressure. What is a safe number of times I could reload before I start turning necks?

[Mark Davis]

GEmanuel is right about outside neck turning for concentricity.
Inside neck reaming is done to thin neck walls that have become to thick, or thinning neck walls that are to thick due to resizing case into another caliber such as .308 reformed to .243.
Can't really say how many times you can reload brass before a problem crops up.
To many varieables, chamber tolerence, brass manafacturing tolerence, brass composition and chamber pressure to name some big ones.

[Mark Davis]

A simple check that only applies only to your rifle and brass fired from your rifle.
With unsized, fired cases see if a bullet will slip through the neck.
If it falls right in no problem.
If it drags you are close to a problem
If it will not go in with finger pressure you have a problem.
The real choke point will be at the top of the shoulder/ bottom of the neck.

[oladcock]

What GE says.... Waste of time for all but the most precise benchrest type shooting. All our AR's will shoot sub-moa and never turned a neck. If that over pressure theory was correct, you'd have a problem between crimping and not crimping which isn't an issue either......O.L.