Case Neck Tension???

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  • Last Post 19 December 2016
yodogsandman posted this 30 November 2016

 I haven't seen much information on case neck tension as it effects shooting cast bullets. How do we measure it? Are newly annealed case necks more consistent than work hardened case necks? How are powder burn rates affected by different “release pressures” from inconsistent case neck tension? Is the only way to measure case neck tension by measuring seating pressure?

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David Reiss posted this 30 November 2016

Case neck tension is directly tied in with accuracy. Annealing if done properly will help to give uniform neck tension and positive uniform, ignition. However if done to the point where the cases are too soft, then it may be difficult to get uniform ignition. As we all know most firearms are unique to themselves and some may shoot better with un-annealed cases. But we all know that annealing helps to lengthen case life. You will just need to experiment with your firearm to see what works best. 

David Reiss - NRA Life Member & PSC Range Member Retired Police Firearms Instructor/Armorer
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Maven posted this 30 November 2016

Wasn't there an article in TFS within the last year or so which questioned the supposedly strong correlation between neck tension and accuracy in rifle cartridges?

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R. Dupraz posted this 30 November 2016

Search the archives. This subject has been discussed at some length in the past. Includes two years of data by a match shooter.

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yodogsandman posted this 30 November 2016

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OU812 posted this 30 November 2016

I have annealed 100 Lapua cases from the same lot and not all had the same tension afterwards. You can feel the difference when using expander ball. Expander balls can come in different sizes if you look hard enough. Hornaday makes a nice tapered .226 expander for 22 caliber that can be polished down if need be..

I like just enough neck tension to chamber my bore rider bullet without it not being pushed back too far into case. Bullet should stop against forcing cone and first drive band after chambering, this is enough for good consistent ignition.

...

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John Alexander posted this 01 December 2016 

             I use about the same approach as OU812 for neck tension.

  There is no doubt that you can have too little neck tension resulting in the bullet being pushed back into the case and not seating into the lands the same each time.  Another possibility is that neck tension may be too low and thus affect the burning rate of some powders.    The tension can also be so tight (common in using dies for JBs) that it damages the bullet by sizing it down, upsetting the nose to a larger diameter, or even bending a long bullet.   So it is possible for neck tension to be either too little or too much and cause trouble.  However, yodogsandman's question that started this thread, at least as I understood it, is about the variation in neck tension causing “different release pressures from inconsistent case neck tension?” This is the variation from one cartridge to the next as felt in resistance at the press lever in seating the bullet.   The effect this round-to-round variation has on either velocity or accuracy is NONE AT ALL.  This isn't just my opinion but the result of excellent experimental work by Gerry Bottiger reported in the Fouling Shot. The bugaboo of round-to-round variation in neck tension is not something we should worry about.   Gerry's work is backed up by looking at the forces involved.  The force caused by neck tension (30 to 80 pounds) is tiny compared to the force on the bullet by the expanding gas (2,000 + pounds).  The possible variation in force by neck tension is even smaller.  For a more complete discussion see the article on page 7 of Fouling Shot #240.   John    

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onondaga posted this 01 December 2016

yodogsandman wrote: Are newly annealed case necks more consistent than work hardened case necks? The key to answering that is right in the question. Consistency can be maintained with persistence of effort throughout reloading in all aspects. A regular regimen of annealing brass is better than none. Opinions vary widely on how many cycles of loading before annealing is best. Opinions are just that without repeatable and measurable consistency. There is nothing inherently wrong with saying I anneal every 7 loading cycles and that gives me good results, but I am not measuring neck tension with a gauge.

The single most thing that gives me consistency in neck tension is brushing inside case necks to remove fouling and polishing compound grit so I can seat bullets into clean shiny brass. If the degree of clean is constant and dies are set to that, results are repeatable. Varying degrees of dirt in the case necks causes fluctuation in neck tension that I can easily observe with no special tools for measuring by just relying on my sense of touch seating bullets. The dirt factor is much easier to feel than where I am in cycles before annealing again. With 7 cycles, I cant feel the difference. One dirty case neck at any cycle, I can easily feel.

Gary

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John Alexander posted this 12 December 2016

I agree with Gary that seating into clean shiny brass will feel more uniform than into not cleaned necks.

The important thing is all this brushing and cleaning is a total waste of time if your concern is that it might affect accuracy or uniform velocity -- it won't.

There are no controlled tests that I know of (educate me if you know of one) that indicate that variations in round to round neck tension has any effect on either accuracy or velocity.

On the other hand Bottiger's excellent work shows that variations in round to round neck tension have no effect on either velocity or accuracy.

One reason that improvement in CB shooting is so slow is that we continue to discuss, worry about, and waste time on busy work that has no effect on shooting results.  Shot to shot variation in neck tension is an excellent example. See “Sniping at Zombies” in Fouling Shot #240 for a discussion.

John

 

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OU812 posted this 13 December 2016

Turning the case necks will help make tension more consistent and help with concentricity (loaded rounds). 

What about using different brands of brass...Remington, Winchester, Lapua. I have all three brands and my Lapua cases have less case wall run out, but are thicker (more difficult to fireform). The Winchesters are next in line as far as case wall run out, and are thinner and easier to fire form.. The  Remington cases have more runout than Lapua and Winchester and are thinner like Winchester. My NECO case gauge allows me to pick the best cases of each brand then I turn the necks to same .010 -.011 thickness.

95 percent of my Lapua cases are uniform with near perfect wall runout (less than .001), but are too thick at shoulder IMO.

30 percent of the Winchester 223 brass of the same lot are close enough to perfect (less than .001 runout).

25 percent of Remington 223 brass of same lot are close enough to perfect. (less than .001 runout)

I try to eliminate bad accuracy variables by using more uniform brass that is weighed, turned necks, chamfered flash hole, trimmed to equal length and equal head space (.000- .003).

Keeping good records of how cases were loaded helps returning to that accurate load. I have failed to do this too many times. I have probably played with sizing and neck tension most and accuracy is never the same afterwards... from my  223 Remington any way?

 

 

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SierraHunter posted this 15 December 2016

I believe consistent neck thickness is much more important then hardness. I've mixed batches of cases that had been fired unknown number of times, but had all had the necks turned on the same machine, and never noticed any difference over batches of cases that had exact same firings from new.

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OU812 posted this 16 December 2016

John mentioned that seating a bullet into a case that has too much neck tension can actually bump or enlarge the bullet diameter  ...especially softer alloys. Sizing bullets base first can cause this also.

Here is proof. Very little arm pressure caused this .224 caliber bullet (13bhn) to grow larger. I did this while experimenting squaring gas checks. Imagine what 20,000 psi chamber pressure could do... exiting the muzzle?

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John Alexander posted this 16 December 2016

SierraHunter,

I am not surprised that you found no difference with necks with differing levels of work hardening.  I think you would find the same for differing neck thicknesses, or for a lot in which the thickness and work harding both varied from one case to the next.  At least I have been reading everything could get my hands on for sixty years and I have never seen a  report giving evidence that it made a bit of difference.

It is possible to have two much neck tension (bullet damage) or too little (not enough to seat bullet consistently.) But if these two conditions are avoided there is solid experimental evidence that round to round inconsistency in neck tension has no effect on either accuracy or velocity -- and no experimental finding to the contrary.

This is what should be expected because the force of gas on the bullet is hundreds of times greater than the tiny variations in neck tension. So it would be amazing if these tiny variations had any effect on anything.

John

 

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SierraHunter posted this 16 December 2016

I don't suppose thickness would make any difference, I was thinking more neck uniformity. If you put a outside neck Turner so that it just touches, and turn the neck, there will usually be spots where it cuts more then others, and even spots where it will not cut at all. So after turning the necks, usually they are a bit more uniform then non turned necks, and I have found that to be slightly more accurate.

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joeb33050 posted this 16 December 2016

Variations in case neck tension do not affect accuracy, based on the available experiment data.

But.

I've been experimenting with nose sizing 22 bullets; this allows the bullet to be seated further out in the case neck into the throat, doing some bore riding, which I think is a good thing.

Variations in bolt closing force finally got me to understand that variations in neck thickness-tension-nose diameter cause variations in seated-in-the-chamber OAL, and reduce accuracy. With enough neck tension the bullet is pushed into the throat. With less neck tension the bullet is pushed back into the case.

I've gone away from nose sizing and seat bullets deep enough to not be pushed back into the case.

I'd be interested in chronograph results at various OALs with same gun/bullet/load, any experimenters out there?

joe b 

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Ken Campbell Iowa posted this 16 December 2016

my current model of neck tension is that the brass neck expands away from the bullet before the bullet moves forward significantly .... thus leaving our near-liquid bullet hanging in mid air and subject to terrible things indeed ... does the gas flow around the floating bullet equally ... ??

..and ” supports  ( g ) ” the concept that the bullet suffers less distortion as it is more and more fully seated into the throat and rifling before ignition .  since long bore-rider noses keep winning matches, maybe the trade-off of ” nose-slumping ” is still less than the good alignment the long nose provides .  i bet somebody might try a total bore-rider except a short groove dia. base just to seat bullet .  might not even need a throat for that chamber .  i am guessing the results would be easy 2 moa groups but no 0.7 groups.  not all bad if that happened ...

*************

regarding neck turning, i think this has to do with holding the base of the bullet more nearly aligned with the throat before ignition . 

the ultimate promise of neck turning is to have the od of the neck fit so tight in the chamber that the bullet thinks it is breech seated ....  this may be a case of too much common sense because tests have been done with extra thick necks ... and results did not show that worthwhile . 

ken

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OU812 posted this 16 December 2016

In cold months my LBT Soft Blue lube thickens in the Lubrisizer. The thicker viscosity causes more pressure being put on nose of bullet resulting in a bore ride section that is .001-.002  larger than before lubing (.sizing die is .0005 larger than bullet). I may purchase a heater for the lubrisizer to make lubing easier on small 224 bullet. Maybe hand dipping or careful tumble lubing is better at reducing distortion for better alignment before bullet distorts on firing...you do not want the bullet tip to wobble in flight.

The last cases I loaded were expanded using a Hornaday .226 neck expander.  The bullet is sized.226 nose first thru  die then hand dipped in Alox (less distortion). Neck tension is lower, but not too low. This allows for easier alignment when the loose fitted bullet is chambered and pushed back further into case. Loose can sometimes be better.

The next bullets will be cast using harder 16bhn alloy nearly equal to Hardball alloy (50/50 linotype and lead). Maybe slightly harder is best?

 

 

 

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GP Idaho posted this 16 December 2016

Joe; As you know we both do quite a bit of 22 shooting using TiteGroup. (You just shoot them into smaller groups) lol  I've also used closing the action to finish seating the bullet but I'm open to the thought there may be a better way.  Weather here in Idaho has taken a turn for the worst, no surprise for December.  But I will load up some 22 rounds in .010  increments from jammed in tight to 20 or 30 off and chronograph the result.  Gp

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SierraHunter posted this 16 December 2016

I've tested this in my 6x45. In that rifle, with the RCBS 95 grain, about .020” off the lands seems to work the best, and shoots much better groups then where the bullet is jammed into the lands.

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OU812 posted this 19 December 2016

John wrote: "The tension can also be so tight (common in using dies for JBs) that it damages the bullet by sizing it down, upsetting the nose to a larger diameter, or even bending a long bullet".   John  
John, Thanks for this verygood little bit of advice. I believe this has been the BIGGEST cause of my accuracy being inconsistent. I  never thought these little soft bullets were so fragile until I measured.
 

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