Neck turning...min neck thickness

[nksmfamjp]

So, I bought some new WSM brass from Winchester. I cleaned up the last set turning to 0.014" neck wall thickness. It comes 0.015 +/- 0.002".....the cleans up most cases 90% or more. ....but some are literally 0.013" at 30% of their circumference....

i could cut to 0.0135" to get closer, but when reloading, I see cracks form at the base of the neck and split necks In 3 loadings. This was before I annealed. After annealing, that has stopped.

My question is thinning the necks to 0.0135"....wont that cause splits quicker? What is your experience turning necks. BTW, I did this originally to get from 0.75" groups to 0.6". I'm hoping the new barrel does similar for me.....but gets me under 0.5" with a low sd (5ish).

 

[243winxb]

Thin doesnt cause splits.

Splits are from over working the brass with a standard sizing die & expander. Try a bushing die.

Or

The chambers neck may be on the large side. Compare a loaded rounds outside neck diameter to the fired brass OD. How much is the neck expanding on firing?

 

[Mikecr]

If you turn so much from necks that already fit the chamber, you'll be over working the necks.
What size is the chamber neck with the new barrel?

 

[nksmfamjp]

If you turn so much from necks that already fit the chamber, you'll be over working the necks.
What size is the chamber neck with the new barrel?

Fired cases measure .346" at the ~mid point with calipers. Loaded rounds measure 0.336".

 

[Varmint Hunter]

In order to accommodate my minimum spec chamber I turn my Win 7WSM cases to .013" and have never had an issue. IIRC that leaves me with .002"-.003" of bullet release. It looks like you're getting at least .010", I'm wondering if that is partially responsible for the cracked necks.

 

[nksmfamjp]

In order to accommodate my minimum spec chamber I turn my Win 7WSM cases to .013" and have never had an issue. IIRC that leaves me with .002"-.003" of bullet release. It looks like you're getting at least .010", I'm wondering if that is partially responsible for the cracked necks.

Cracked necks were in the factory barrel...might have been bigger.

 

[Mikecr]

Well, you gotta know that 11thou of neck clearance (chamber neck (-) spring back to .346)(-)(.336) is excessive.
Do you think there is no price for that?
Do you think that you're actually improving anything with turning here?

 

[nksmfamjp]

Well, you gotta know that 11thou of neck clearance (chamber neck (-) spring back to .346)(-)(.336) is excessive.
Do you think there is no price for that?
Do you think that you're actually improving anything with turning here?

I don't know....dropped group size 0.15" in the original barrel...that seems like something. Your thoughts? I could have become a better shooter....

 

[MNbogboy]

A couple of points;
1. Depending on your sizing die, turning the necks will affect "neck tension/grip" which in turn may have improved the rounds precision. With bushing dies the same or close to the same thing could have been accomplished with bushing size.
2. Your annealing has probably had the most influence on not cracking necks.
Skim turning to remove thin spots in lesser quality brass will actually help prevent neck splitting. Necks will stretch more at the thinner spots. The thinning gets worse with each firing. Sizing/expanding works the thinner spots even more. So yes, turning can help with neck overworking up to a point.
Turning them thin in a no-turn chamber makes little sense.
3. Common "less expensive" brass can be checked with a ball-mike for variation and turned accordingly. Sometimes it will not clean up perfect. Neck seal is sometimes affected (usually to the good) by any turning.
But turning too much with a bullet that is seated shallow in the neck can contort the brass in the pressure cycle to seal farther back and "lift" the case mouth itself causing poor or late seal and carbon buildup. This can be noticed by checking fired cases with a new bullet, the bullet does not want to start in the case mouth or is tight just on the outside of the case mouth.
4. Also I have found a lot of the brass I use in that .0135 - .0150 category. .0135 is usually where I shoot for and end up but these are for all saami chambers (and that factory stuff is on the saami "big" end.
My .02,

 

[Frank Kalisz]

I turn my Lapua and military 308 brasses to 0.014" using Forster "Original" hand lathe. Based on my Starrett ball micrometer, my turning is pretty accurate.

 

[Don Garlow]

This is an interesting topic for me because I've always wondered how to determine the actual neck diameter in a rifle's chamber so that case necks can be trued without removing excess material and causing the necks to over expand upon firing. I do use bushing dies but have still experience neck cracking with cases turned to 0.014 thickness. SO.....How do you positively determine the neck diameter of the chamber? Will measuring the reamer provide the data on a custom build?

 

[Frank Kalisz]

SO.....How do you positively determine the neck diameter of the chamber? Will measuring the reamer provide the data on a custom build?

I rely on measuring brass after it's fireformed. I use my Mitutoyu Dial Caliper to measure outside diameters, I use my Starrett Ball Micrometer to measure neck wall thickness, and I use pin gauges to measure interior neck diameters.

 

[Frank Kalisz]

Don,
My understanding is 14thou is a pretty standard thickness for brass necks. If you're still having problems with necks cracking, I can only suggest looking at your annealing and quality of your brass. Good Luck to you!
P.S. - What cartridge are you using?

 

[ntsqd]

The best way that I know of to determine what the chamber neck size is, would be to take a casting of it. A fired case is going to have spring-back in it and won't tell you the exact neck size in the chamber. For example, even if you spec'd a .268" neck in your .243 AI chamber how do you know that is what you got? It might have been reamed .272".....

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