How thin to neck turn?

[Viperdoc]

Have been measuring necks on Hornady 6.5 Creedmore brass, and they seem to vary between 0.0145 to 0.0125 using a tubing gauge. I turned them down to around 0.013, which meant around 2/3's of each neck was trimmed in circumference (they now range from a few low spots at 0.0125 to a high of 0.0135, but most of the circumference is right at 0.013). Taking it down further by turning the entire neck to 0.0125 would make the tolerance and run out better of course.

How much is too thin in a mid sized caliber like 6.5CM?

How will it affect neck life and splitting, and how much run out is acceptable before seeing a decline in accuracy?

I recognize there are probably no exact answers, but looking for opinions. The rifle is mostly used for long range target shooting and PD's- 300 plus yards. Mostly shooting Berger 140 VLD but anticipate trying the 130's.

 

[mikecr]

That's a fairly big variance(2thou). Are you SURE on that?
Do you set a datum of neck thickness measure with a stop on your mic?

Would your chamber neck clearances lead to huge over-working/sizing at 12.5thou?
If not, there is nothing 'wrong' in this thickness, and you can still get plenty of tension & life from it.

 

[fdshuster]

Viperdoc: I usually base my neck turning thickness requirements of the chamber neck diameter. Don't like to see much more than .003" less than chamber neck dia.

One of my chambers has a .251" neck dia., loaded round is .248", necks are turned to .012" x 2 = .024" + .224" bullet dia. = .248". Neck bushing is .247", so the brass is being "worked" a total of .004", one of the reasons it last for 40+ loadings.

The more brass is removed, the sloppier the fit between the case & chamber walls.

I guess the main question is: what is your chamber neck dia, and the loaded round neck diameter, without turning?

 

[Viperdoc]

Diameter of loaded and not turned round is 0.290

I resized all (500 or so) of my once fired brass, but seem to recall 0.294 as the diameter of a fired round, so chamber is probably 0.295 or 0.296

Diameter of turned round should end up around 0.288-0.289. So, brass might be going 0.296-0.288 or 0.008 as a maximum change.

I was thinking about having a reamer made based upon a slightly tighter neck. Also probably no throat as well so I can get VLD's into the lands out of a mag.

 

[Viperdoc]

Probably should also mention using either 0.284 or 0.285 bushing, which give a little spring back, around 0.001. Neck tension ends up being around 0.003.