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To turn or not (necks)

 
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  #22  
Old 04-23-2009, 07:13 AM
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Re: To turn or not (necks)

Sizing without the expander will improve runout or concentricity. When you pull the expander back through the neck it can and often does create runout. Also if you size without the expander then you do not have to lube the inside of the neck.

When you take the expander out and turn the necks you can take the brass neck thickness down to a specific thickness so that you do not have too much bullet grip. For instance if you have a 30-06 full length die and take the expander out and size the case and the outside of the neck measures .329" and your neck thickness is .014" then the math would be

.329" - .014" -.014" = .301"

that is too much bullet grip of .308" - .301" = .007"

But if you neck turned your brass down to .012" the math would be

.329" - .012" -.012" = .305"

which is about right for a bullet grip of .308" - .305" = .003"

There are ways to minimize the bad effects of the expander but I am no expert in that since I just don't use them.
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  #23  
Old 04-23-2009, 09:11 AM
tlk tlk is offline
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Re: To turn or not (necks)

Woods, you are equating the difference in bullet o.d. to case mouth i.d. to a force (bullet grip). Can you give some more info on this? How is .007" too much grip but .003" is just right? How is this quantified and where can I get this data? If I think about this I can see a graph with at least two curves and an intesection point.
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  #24  
Old 04-23-2009, 10:34 AM
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Re: To turn or not (necks)

I do exactly what woods is proposing for some of my loads. (i.e. neck turning and using standard dies). This works great to control neck tension, and I too shoot for that 0.003 - 0.004 thou neck tension.

The downside is that you wind up working the brass more. Here is what I mean. Every shot fired , the neck expands more (because brass from the neck has been removed) and every time you resize, the die has to size down the neck farther because it expanded farther. This causes additional work hardening of each case every time it is fired and resized and shortens brass life. "No big deal"... IF you anneal the brass every 3-4 firings.

Neck turning is fast and easy and nobody should shy away from it. It is an excellent tool when used properly it WILL help accuracy regardless of the chambering (factory/custom) of your rifle. Neck turning is the only way to ensure uniform neck tension. If a batch of cases has even 0.001 - 0.002 thou difference in neck thickness, then you will have at least 0.001 - 0.002 thou variation in neck tension which has been proven to increase ES and SD at the muzzle!

Here is a link that I think explains it all:

Outside Case Neck Turning for Factory Rifles | The Reloading Press
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  #25  
Old 04-23-2009, 11:34 AM
tlk tlk is offline
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Re: To turn or not (necks)

Quote:
Originally Posted by nheninge View Post
neck turning does NOT center the bullets/necks. To be truley centered, a case must first have zero neck variance. So... the only way to center a case is to sort by case neck variance (using only cases with zero variance), and then neck turn for uniform neck tension. If a case neck has 2.5 thou variance, then it has a thick side and a thin side and the bullet/neck has to sit closer to the thin side (thus offset from the bore). All the neck turning in the world will not change the fact that the bullet/neck is offset if you start with a case that is offset
Nheninge, I don't get something: If I turn the outside of the neck, doesn't that get rid of any thick/thin variation since I am taking off metal from the outside relative to the inside diameter?

After turning, the thickness should be a constant from the inside of the case mouth to the outside of it UNLESS the mouth is thinner in some spots than the cutter is set at. This is the only time the cutter would not correct the variance that I can think of. Is this what you mean by sorting cases based on variance: you are sorting based on case neck walls that are thinner than what you will be turning them down to? And in any event, wont this turning help even those that are that thin since it reduce the amount of variance?

Thanks.
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  #26  
Old 04-23-2009, 03:40 PM
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Re: To turn or not (necks)

My neighbor used to shoot competitive benchrest and tested the theory of whether turning actually made a difference in a rail gun. He shot turned necks and unturned necks and could not tell the difference. He doesn't turn necks anymore.
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  #27  
Old 04-23-2009, 04:51 PM
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Re: To turn or not (necks)



Here is my attempt to explain...

Not to scale and all numbers are random

Neck turning uniforms the case neck thickness, but not the center of its axis, thus making a case with neck variance "offset from the get go" regardless of turning.

I can guarantee that turning necks does make a difference because it also uniforms neck tension. So unless you want to use a different sizing bushing for every shell or only use cases with exactly the same thickness and no neck variance... neck turning is the way to go.
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  #28  
Old 04-23-2009, 06:21 PM
tlk tlk is offline
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Re: To turn or not (necks)

That explains it. Thanks for the illustration.

And leads to my next question: If you f/l size does this negate any of the effects of a case that is variable in thickness?

What I mean is that if the neck is turned we are good there. If the case is f/l sized then the OD is good - any variation is with the I.D. In this case wouldn't the center of the case and the center of the neck be the same?

I am still thinking this one through.
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