Neck Turning Question

[TimP]

I am in the process of neck turning some 7x57 Mauser brass for a (.274 neck) 6mm AI chamber. I am turning the necks to .014 per side and cutting into the shoulder about a 32nd of an inch.When I measure the turned neck starting at the case mouth and work up to the shoulder I am getting larger measurement close to the shoulder neck junction.The measurement is consistend until I get close to the shoulder where it increases to .01450 - .01460. I loaded a couple of dummy rounds and I am at .271 until I get closer to the shoulder where my measurement increases again. Now correct me if I am wrong but when I fire form the AI the shoulder will blow out past this point and the neck will shorten. If that's the case this may not be a problem for this cartridge but what about a non AI type cartridge.
I am using Sinclair's NT 4000 turner and wondering if there is something wrong with the tool or is this typical. I would think that the neck after turning would be a consistent measurement right up to the shoulder.

 

[DennisH]

The only thing i can tell you is I don't turn into the shoulder. I say away at least 1/32 from the shoulder and after firing the first time, only trained eyes can see where I stopped.

The measurement is consistend until I get close to the shoulder where it increases

How "close" are you to the shoulder before you start seeing a difference?

 

[M14AMU]

It might pay you to read this:

http://riflemansjournal.blogspot.com/2009/12/reloading-neck-turning.html

 

[TimP]

DennisH

How "close" are you to the shoulder before you start seeing a difference?

Close just below the shoulder neck junction.

RMulheim

Thanks for the article.

 

[DennisH]

DennisH

How "close" are you to the shoulder before you start seeing a difference?

About 1/32" where the shoulder starts. I will see if I can get a good picture and post it.

 

[TimP]

DennisH

How "close" are you to the shoulder before you start seeing a difference?

About 1/32" where the shoulder starts. I will see if I can get a good picture and post it.

DennisH, thanks for the reply.

I am cutting into the shoulder about1/32" you can clearly see the ring. What I couldn't figure out is why my case neck is thicker just below the neck shoulder junction than it is at the most of the case neck length. I called Sinclair today and talked to one of there Tec's and was told this was typical. Either way I still have enough neck clearance. Just not sure why it wouldn't cut square right up to the neck/shoulder junction.

 

[LHSmith]

Unless you are machinist or QA parts inspector you will drive yourself nuts miking the neck wall thickness. Turn the necks thin enough that a LOADED round fits your chamber with at least .0015 radial clearance (.003 total) along the entire length of the neck and forget the neck wall reading variations. What make turner? There was one brand that could cut a taper.

 

[TimP]

Unless you are machinist or QA parts inspector you will drive yourself nuts miking the neck wall thickness. Turn the necks thin enough that a LOADED round fits your chamber with at least .0015 radial clearance (.003 total) along the entire length of the neck and forget the neck wall reading variations. What make turner? There was one brand that could cut a taper.

Sinclair's NT-4000. My loaded round measures .27090 over most of the neck length. But as I get close to the neck/shoulder junction it increases about .001. It's a .274 neck so that still leaves me with .002 worse case so I am running with it. When I FF the 40 degree shoulder the thicker brass will be in the shoulder.

Thanks for everbody's advice.

 

[gotcha]

Tim, Most chamber reamers cut a taper in the neck anywhere from .001" to .002" dia. The mouth of the chamber being a smaller Dia. If your chamber reamer followed the 6 Rem. spec for taper there will be .0011" larger I.D. @ neck shoulder than @ mouth of chamber. If you size the neck w/ an expander or, say, A collet die. Any neck wall inconsistency you MIGHT have will be pushed to the outside of the neck wall. There is .016" difference between 6AI & 7X57 (Base to nk shoulder) So, I agree. You should be golden....... If all else fails you can always use 6mm Rem. brass. Thats what I ended up doing about 20 years ago when I built a 6AI I wasn't as smart as you.