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To turn or not (necks)

 
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  #36  
Old 04-25-2009, 11:17 AM
tlk tlk is offline
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Re: To turn or not (necks)

Quote:
Originally Posted by woods View Post
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"

When you compared thickness to grip I took it to mean that there is a quantifiable holding force involved of some value (lbs, etc).

Part of this probably is overboard. I just put my entire thought process down for verification. Maybe all I accomplished was showing what I think on in my free time in the car .

Last edited by tlk; 04-25-2009 at 12:52 PM.
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  #37  
Old 04-25-2009, 01:05 PM
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Re: To turn or not (necks)

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Originally Posted by tlk View Post
Maybe all I accomplished was showing what I think on in my free time in the car .
Man's gotta have something to think about while driving down the freeway!

Where the difference lies with respect to neck thickness and bullet grip is that the bullet grip is not derived from the neck thickness itself but rather from the inside diameter of the neck. IOW if you had 2 cases both with an inside diameter .003" less than caliber and 1 had a consistant neck thickness of .014" and the other had a consistant neck thickness of .012", there probably would be a difference in bullet grip but it would be unmeasureable, undetectable and of no significance compared to varying the inside diameter by even a small amount, like .0025".

Previously I had not sorted by neck variance but I will try it with the next batch of new brass before I neck turn. Seems to me that if the manufacturing process could make a piece of brass with a variance in neck thickness then it would be possible to make one with the neck out of center with regard to the center of the case body also.
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  #38  
Old 04-25-2009, 02:18 PM
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Re: To turn or not (necks)

Quote:
IOW if you had 2 cases both with an inside diameter .003" less than caliber and 1 had a consistant neck thickness of .014" and the other had a consistant neck thickness of .012", there probably would be a difference in bullet grip but it would be unmeasureable, undetectable and of no significance compared to varying the inside diameter by even a small amount, like .0025".
Not true at all.

Take the KM arbor press with the dial indicator on top and inline die and you can see, measure and feel the difference. No dial indicator and you can certainly feel the difference when seating. That is routinely used for neck turned brass for 1k BR shooters to sort rounds as loading for "match" or "sighter" category.

BH
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  #39  
Old 04-25-2009, 02:37 PM
tlk tlk is offline
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Re: To turn or not (necks)

Woods, I re-read your post I quoted, and see what you were saying: you are sizing off of the outside. If you size off of the outside (no expander ball)and turn the neck down you are changing the I.D. of the case neck. So instead of relying upon an expander ball, you can customize bullet grip by turning necks to various thicknesses and relying upon the die to size the outside. Didn't see that important detail before. See, this is what I mean by re-reading everything - details can get missed easily.

Can someone hand me a skillet so I can scramble this egg on my face?
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  #40  
Old 04-25-2009, 04:21 PM
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Re: To turn or not (necks)

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Originally Posted by BountyHunter View Post
Not true at all.

Take the KM arbor press with the dial indicator on top and inline die and you can see, measure and feel the difference. No dial indicator and you can certainly feel the difference when seating. That is routinely used for neck turned brass for 1k BR shooters to sort rounds as loading for "match" or "sighter" category.

BH
Possibly.

IME there is a definite increase in seating pressure when going from one bushing size to another in a bushing neck sizer and also when using different size mandrels that I ordered from Lee for the Lee Collet neck sizer. IOW, by changing the bullet grip. By contrast when I have sized cases with the Lee Collet for a factory rifle on cases that I have not neck turned, I can get consistant seating force even though there are neck thickness variances. However the Lee Collet mandrel I normally use for factory rifles gives only .001" bullet grip so that may have some bearing on the seating force.

Differences in seating force IME (after standardizing the ID) has been much more dependent upon the condition of the inside of the neck. On mine I use no lube, scour the inside with scotchbrite, smooth the inside with steel wool and then use mica



in order to make for as consistant seating force as possible.

So I get consistant seating force with cases I have not neck turned and I get consistant seating force with cases that I have neck turned. IME the seating force changes noticeably with changes in bullet grip.
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  #41  
Old 04-25-2009, 09:25 PM
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Re: To turn or not (necks)

The K&m arbor with force measurement is great (I also use it routinely) but it is also an indirect measurement consisting of many factors including: neck tension, neck thickness, neck uniformity/neck imperfections, lubrication, bullet shape etc. "Seating force" is the best measurement we have to measure these variations in case prep when seating bullets.

I returned my RCBS casemaster waaaaaay back. Just felt cheap, and that bushing neck thickness thing had way too much play for my liking. It just felt like it was built by the lowest bidder.

I did verify the case thickness throughout the case with the RCBS tool though. I modified a bar to fit in the tool similiar to the case head separation bar (just long enough to fit in the neck and still make contact with the inside of the brass) and found thick/thin sides consistently down the length of the cases at the same spot represented on the neck. This is fact. And the banana case theory has quite a bit of discussion/research as well. This theory's effects are mostly negated "IF" you sort by neck variation. I still index my cases squarely behind the recoil lug (which makes no sense) but I guess I do this because it is consistent.

I think in the car too. Hope we all never meet while driving or we may CRASH!!!
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