Long Range Hunting Online Magazine


Go Back   Long Range Hunting Online Magazine > Rifles, Reloading, Optics, Equipment > Reloading

Reloading Techniques For Reloading


Reply

To turn or not (necks)

 
LinkBack Thread Tools Display Modes
  #29  
Old 04-23-2009, 07:13 PM
Silver Member
 
Join Date: Oct 2008
Location: Bryan, Tx
Posts: 284
Re: To turn or not (necks)

Yes, I think fire forming followed by FL resizing should reset this difference because your dies body/shoulder/neck are drilled/honed with concentric bits and should have a single axis if they are quality dies.

However, thick/thin sides run the length of the case. This is only noticed if ID measurements of variance are taken.

I find a lot of value in culling cases with increased neck variance. If I get 200 good cases with no variance (followed by neck turning), those 200 cases may last the life of the barrel if the brass is treated properly. A lot of concentricity/runout problems are avoided since I never start with a problem.
Reply With Quote
  #30  
Old 04-23-2009, 09:36 PM
Gold Member
 
Join Date: Jun 2006
Location: Shangri-La
Posts: 912
Re: To turn or not (necks)

Good stuff!

How do you sort for neck thickness variations? Do you use a ball micrometer?



With brass as hard to come by lately it would hurt to have to throw some away.
__________________
If you can read this, thank a teacher.......if you are reading this in English, thank a soldier.
Reply With Quote
  #31  
Old 04-23-2009, 10:24 PM
Silver Member
 
Join Date: Oct 2008
Location: Bryan, Tx
Posts: 284
Re: To turn or not (necks)

I sort neck thickness variation with the Sinclair tool. It has a pilot stop for each caliber that fits perfectly after using an expander mandrel (to round the necks on new brass. Then you spin the cases by hand and read the variation on a dial mic.

[IMG]file:///C:/DOCUME%7E1/NOAHH%7E1/LOCALS%7E1/Temp/moz-screenshot.jpg[/IMG]

Thick and thin sides can be marked easily for indexing
A ball mic w/ stand and feeler gauges are used to verify thickness

I know brass is expensive, but so is a miss...
Reply With Quote
  #32  
Old 04-24-2009, 07:22 AM
tlk tlk is offline
Silver Member
 
Join Date: Apr 2008
Posts: 238
Re: To turn or not (necks)

I am using an RCBS case master guaging tool, and I dont think I am too happy with it as it is. It works similiar to the Sinclair tool, but there is a bushing that slips on top of the case neck. You measure off of this bushing, but I found it to vary up to .003" in places if you roll it instead of just take specific data points. I think that if I took the bushing to my local machinist and had it smoothed out it would be fine. Probably will do that. Or I will get a good ball micrometer as I suspect the cost will be the same.
Reply With Quote
  #33  
Old 04-24-2009, 08:51 AM
tlk tlk is offline
Silver Member
 
Join Date: Apr 2008
Posts: 238
Re: To turn or not (necks)

OK, I think I found a problem: If the brass is f/l sized as stated before and everything is centered, neck is turned, etc., what happens to the brass upon firing?

Will the thin portions of the case body expand faster than the thicker and cause the case to swell into the chamber at an uneven rate around the case body? If so, will this cause the bullet to no longer be aligned by the time pressure has built up enough to get it out of the case and into the barrel? Is the case thickness variation causing innacuracy in this case? Somewhat difficult to explain what I am talking about, but I am thinking that the uneven expansion might have an effect by placing leveraging force on the shoulder/case mouth.

But would it? Would it matter if you had the case body smaller than the chamber and the whole case pinned between a trued boltface and the datum? I wonder with this being the situation if the shoulder being a slight crush fit would help prevent/minimize this issue.
Reply With Quote
  #34  
Old 04-25-2009, 09:06 AM
tlk tlk is offline
Silver Member
 
Join Date: Apr 2008
Posts: 238
Re: To turn or not (necks)

Still working on this one, let me know if these thoughts are correct:

If your brass is slightly crush fit (as per above with the case body smaller than the chamber), then the only time that the thickness variation of a case body would matter would be IF the case body wasn't finished expanding by the time the bullet began leaving the neck, which may negate any advantages to neck sizing because it would cause the bullet to be off-center again as it moved into the rifling.

The question is if the pressure required to launch the bullet out of the case mouth is greater than the pressure to expand the case itself. If it is less, then the bullet could leave before any case expansion occurs, giving you the full advatage of the trued neck. Same thing would happen for the bullet leaving after the case had fully expanded, since it would be leaving after the case would be at an O.D. equal to the chamber and all of the inaccuracies in thickness variation are back to the inside of the case (during expansion it is moving both to the inside and outside as the case expands from the inside). But pressure would be higher than a lower neck tension because you need to have the bullet hold until ALL of the brass is expanded to the chamber.

----------
The real issue is when the bullet leaves the imperfect (but f/l sized) case that has started expanding but has not finished. Any off-center expansion could be transferred to the bullet. Also, inconsistency for the same case at different reloadings could be thrown into the mix because the case is not in the exact same position each time in the chamber, causing the "off-center" of the bullet to not the the same shot to shot (could be off-center at the 4 o'clock position, next reloading at the 8 o'clock, etc - rotation of the case in the chamber).
----------

If I look at it like this, it means to me that neck turning serves two purposes on the imperfect case: alignment and neck tension, but the bullet must leave at a certain time for it to be advantageous. For nheninge's perfect cases, it serves only for neck tension, and bullet launch can be at any time.

I think I see now why neck turning is not a "nit". Please correct any wrong assumptions in all of this. I want to get this right so we all know.

Woods, I still would like to know how the relation of case neck thickness to neck tension is derived. Is there research or numbers somewhere?


TLK

Last edited by tlk; 04-25-2009 at 09:59 AM.
Reply With Quote
  #35  
Old 04-25-2009, 09:59 AM
Gold Member
 
Join Date: Jun 2006
Location: Shangri-La
Posts: 912
Re: To turn or not (necks)

I think we are well past the simple basics of internal ballistics and reloading here and are operating on theory, sorta like how they discovered black holes with lack of direct evidence but with the combination of theories and implied influences. Almost all this is not verifiable with direct measurement and at best is an educated theory.

Also we are down to minutiae (sp?) when it comes to what the sequence of events is in the milliseconds of the firing sequence. The variance in neck thickness is one of the larger and more verifiable things that we are talking about here and thus may be one of the last controllable things that you can do that will have any significant and identifiable effects on consistancy of the bullet release and firing sequence.

"Woods, I still would like to know how the relation of case neck thickness to neck tension is derived. Is there research or numbers somewhere?"

I'm not sure where I have said that the brass thickness at the neck has a direct correlation to neck tension. What I'm sure I have said somewhere is that you can vary the neck tension (inside diameter) by sizing the entire neck to a smaller dimension. Also I do believe that if you have thicker brass on one side of the neck then that brass will resist stetching from the bullet seating more than the thin side and cant the bullet (runout) and that the thicker brass will expand to the chamber walls slower than the thinner side during the firing sequence. But I do not believe that these effects (other than the runout) will have a large enough significance to make an identifiable significance on paper.

Like nheninge said the cases with identifiable neck thickness variations have those same thickness variations carried down through the case body (also something taken on faith since I have not seen proof of this). It may be possible if this is true that in severe cases you will have a dissimilar expansion and a sort of bannana effect upon firing.

If anyone has a link it would be interesting and informative to this discussion to see the actual formation process of the brass by the manufacturer.
__________________
If you can read this, thank a teacher.......if you are reading this in English, thank a soldier.
Reply With Quote
Reply

Bookmarks

Thread Tools
Display Modes


Similar Threads for: To turn or not (necks)
Thread Thread Starter Forum Replies Last Post
turn necks before fire forming an ackley improved 1sniper Reloading 8 07-10-2011 01:11 AM
Turn necks on virgin brass? Tikka Lover Reloading 4 05-10-2009 11:30 AM
When to turn heikki02003 Reloading 19 02-15-2009 12:39 AM
Do I turn necks are aneal the brass. Iron Worker Reloading 5 09-25-2006 08:06 AM
How much to turn necks? Alan Griffith Reloading 21 06-29-2006 07:54 PM

Current Poll
Do You Think Slingshots Should Be Legalized For Hunting Brown Bear?
Yes - 47.51%
840 Votes
No - 52.49%
928 Votes
Total Votes: 1,768
You may not vote on this poll.

All times are GMT -5. The time now is 06:56 AM.


Powered by vBulletin ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Management Powered by vBadvanced CMPS
All content ©2010-2014 Long Range Hunting, LLC