Neck Tension vs. Time

[Swan]

Happened across this interesting little bit over on the 6mmBR site, not sure if its been posted here before (it's from '08), but anyway:


" TECH TIP–Neck Tension vs. Time
This may surprise you. We’ve learned that time (between neck-sizing operation and bullet seating) can have dramatic effects on neck tension. Controlling neck tension on your cases is a very, very important element of precision reloading. When neck tension is very uniform across all your brass, you’ll see dramatic improvements in ES and SD, and your groups will shrink. Typically you’ll also see fewer fliers. Right now, most reloaders attempt to control neck tension by using different sized neck bushings. This does, indeed, affect how firmly the neck grips your bullets. But time of loading is another key variable.

James Phillips discovered that time is a critical factor in neck tension. James loaded two sets of 22 Dasher brass. Each had been sized with the SAME bushing, however the first group was sized two weeks before loading, whereas the second group was neck-sized just the day before. James noticed immediately that the bullet seating effort was not the same for both sets of cases — not even close.

Using a K&M Arbor press equipped with the optional Bullet-Seating Force Gauge, James determined that over twice as much force was required to seat the bullets which had been neck-sized two weeks before. The dial read-out of seating force for the “older” cases was in the 60s, while the seating force for the recently-neck-sized cases was in the 20s. (These numbers correspond to pounds of force applied to the bullet). Conclusion? In the two weeks that had elapsed since neck-sizing, the necks continued to get tighter and stiffen.

Lesson learned: For match rounds, size ALL your cases at the same time. If you want to reduce neck tension, load immediately after sizing."

While not absolutely conclusive, intriguing nonetheless.

 

[clmayfield]

Re: Neck Tension vs. Time

I had read this before. The key here is to be consistent and segregate cases that are neck sized on different days.

 

[Tangodown911]

Re: Neck Tension vs. Time

If that is the case then it would be reasonable to say that the longer a loaded round sits before it is fired the more the necks tighten as well.

 

[Swan]

Re: Neck Tension vs. Time

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tangodown911</div><div class="ubbcode-body">If that is the case then it would be reasonable to say that the longer a loaded round sits before it is fired the more the necks tighten as well. </div></div>

... same thought crossed my mind after I read it as well.

 

[ReaperDriver]

Re: Neck Tension vs. Time

Cool, now I can make a case to the wife that my staying up late until 1am in the garage reloading the night before I shoot is actually making a difference in my performance.

 

[SPAK]

Re: Neck Tension vs. Time

Has anyone ever had a difference in ammo performance between rounds loaded the day of, night before, two weeks or more prior to shooting?? Just wondering if anyone has any anectdotal data.

 

[ChrisGarrett]

Re: Neck Tension vs. Time

I wonder if it has anything to do with oxidation forming on the inside of the necks and creating more friction?

You'd have to do some serious testing on the elasticity of the cases, before you could say that it's changing at the molecular level, if you ask me.

Chris

 

[Greg Langelius *]

Re: Neck Tension vs. Time

Theoretically, the necks would continue to spring back whether the bullets are seated now or later. It might make some difference whether the bullets are seated now or later.

I make an effort to manage match ammunition neck tension based not on bushing diameter, but rather on neck resizing length. I back off my F/L die so it only resizes a portion of the neck's tip, and use the neck expander ball to ensure the entire neck is expanded prior to resizing the tip of the neck.

My neck tension criterion is 'enough'.

My neck tension criterion is based on being able to rotate the seated bullet in the case neck, using thumb and forefinger. I back off the die with each loading batch and re-advance it until the bullet <span style="font-style: italic"><span style="font-weight: bold">fails</span></span> to turn under the above manual manipulation.

My most recent reloading sesson involved 3x fired Remington .222 Rem brass and Nosler 50gr Ballistic Tip bullets. The neck is sized for approximately the last .065" from the extreme end. The bullet will not spin in the neck, but can be pushed into the case under significantly firm pressure. The ammo is single loaded/hand fed in an M700 action.

I always resize the necks and seat the bullets in the same session, and make a serious effort to only load as much ammo as I will need in the following 2-3 weeks, mainly to preclude oxidation/cold soldering issues.

If the brass needs a bump it gets it, but is then treated as fired brass and the same die height/neck length relationship is re-established for the particular loading session, same as always.

Greg

 

[Low Sioux]

Re: Neck Tension vs. Time

The $64k question is did it affect accuracy ie vertical? If it did how much? What is significant to a world class bench rest shooter is noise in this game. just something to think about.

 

[ChrisGarrett]

Re: Neck Tension vs. Time

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Low Sioux</div><div class="ubbcode-body">The $64k question is did it affect accuracy ie vertical? If it did how much? What is significant to a world class bench rest shooter is noise in this game. just something to think about. </div></div>

I would have liked to have seem some chrono data. More neck tension will grip the bullet more firmly, allowing the bullet to be held in place a bit longer, while the pressure builds up. Presumably, one would get higher velocities and this could be measured.

Chris

 

[ReaperDriver]

Re: Neck Tension vs. Time

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ChrisGarrett</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Low Sioux</div><div class="ubbcode-body">The $64k question is did it affect accuracy ie vertical? If it did how much? What is significant to a world class bench rest shooter is noise in this game. just something to think about. </div></div>

I would have liked to have seem some chrono data. More neck tension will grip the bullet more firmly, allowing the bullet to be held in place a bit longer, while the pressure builds up. Presumably, one would get higher velocities and this could be measured.

Chris </div></div>

I would think for this to be measurable with a chrono, you would have to have some pretty amazingly low ES's to start out with for it to be visible. Otherwise it would hide in the ES overlaps, me thinks. I agree with the earlier poster that verticle dispersion at longer ranges might show the effects more easily than anything else.

 

[Greg Langelius *]

Re: Neck Tension vs. Time

My experiments with neck tension suggest that the best tension is the least, as long as the bullet OAL isn't going to be disturbed by normal handling. While this is a personal opinion, it seems to me I've heard vaguely similar elsewhere down through the ages.

 

[alf]

Re: Neck Tension vs. Time

My take on it based on shooting 1K BR.

I know some are anal enough to not seat their bullets till the morning on match day. I found that it doesn't make any difference, although I do shoot moly, whether that makes a difference or not.

One year, at our April match, I shot ammo that had been loaded from the previous Aug. First group out of the gate was a screamer(under 4.00"). Ever since then I load my ammo when I had time, not a day or two before hand, and worry about the other things that really make a difference.

But then I do try to do things in batches, as in anneal all at the same time, or size, or seat, etc.

 

[clmayfield]

Re: Neck Tension vs. Time

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: alf</div><div class="ubbcode-body">
But then I do try to do things in batches, as in anneal all at the same time, or size, or seat, etc.</div></div>

I think that is the key right there. Neck tension can be higher or lower, but as long as it is consistent on a given day, that matters more than whether it is higher or lower for a given batch.

 

[Country]

Re: Neck Tension vs. Time

Age hardening of brass causes the neck to shink tighter around the projectile. Well annealed cases will take longer to change than already hard brass. It takes only fractional changes to affect neck tension and it's not even around the neck diameter either. Done a 10 year trial on reloads and got some dramatic results but posting pictures on this site is a pain.
Necks so shrunken that it was easy to see with the naked eye.
Stress corrosion was involved also after 10 years.
If anyone wants the photos PM me your email.
Moly does help reduce variations caused by age hardening in long term stored ammo.
I figured out how to post a picture I think!
Some effects of long term storage of loaded rounds.
I recently completed a 10 year trail of the effects of long term storage of loaded rounds . The main focus was on changes to neck tension and bullet grip in general as a result of age hardening .
The tests are not scientific in nature but do show some fairly clear conclusions regarding , changes in neck tension , neck welding and brass shrinkage .

The ammo was 254 rounds of 22-250 Rem in several different brands of cases. These cases were not new and had been fired 6 times. They were loaded with a 55 grain jacketed bullet and a normal powder load .
All case necks were cleaned before any seating.
Annealing of brass was not done to make sure that maximum age hardening took place.
Some bullets were uncoated some were home moly MOs2 coated .
Some were seated without any internal neck lube and some were seated with internal neck lube.
Internal neck lube was a mixture of 50% moly and 50% aluminiumised lock graphite. Rubbed into the inside neck with a cotton bud .
Bullets were marked to identify lubed necks.
Storage was in fairly air tight military ammo box’s however over the 10 years they were moved about a bit so temperatures would have been variable.
Pulling of the projectiles was done by two methods as required.
Kinetic bullet puller and press collet puller.
Bullets were pulled in small batches at a time of each sample against each other so a comparison difference was more noticeable and obvious.
External Inspection .
This showed some weird results . Most case necks with any of the coated or uncoated or lubricated bullets showed the case neck had shrunk in diameter below the base of the bullet and was exerting extreme neck tension.
The amount was quite easy to see . See Photo NW3 and NW4 .
On some of the uncoated bullets a slight brass case colour was evident on the bullet coming up from inside the case mouth . See Photo NW3 uncoated bullet right in the front edge of the case mouth.
This also happened on other parts of uncoated bullets . See photo NW2 .
These uncoated bullets were the hardest to pull and most took 4 or more blows with the KBP . Only a few took 2 or three blows.
Some would not pull at all and had to be extracted with the collet puller.


These very hard to pull bullets would have raised chamber pressures significantly.
Some necks appeared to have white corrosion in them at the base of the bullet and streaks down the inside of the neck. See Photo NW5. These case necks had lost all their clean shine on the inside.
Not sure exactly what this is but it was most prevalent in the cases with uncoated bullets however some cases with coated bullets and neck lube showed traces but not as bad.
It might be air & moisture leaching in along the inside of the case neck and reacting with the powder in some way more at the base of the bullet or reacting between the bullet and the case .
The coating and neck lube may have sealed the neck a bit better reducing this effect.
Military rounds usually have a sealer inside the case neck . I think I now, know why.

As pulling bullets proceeded it became quite clear that the coated and inside neck lubed bullets displayed the most consistent neck tension on average. Even though that tension would have been greater than when it was reloaded.
Requiring only 1 to 2 blows to extract and none requiring the collet puller.
Even though some still had the shrunken neck diameter from brass ageing .
See Photo NW1 .
None of the coated bullets with or without inside neck lube had any sign of true neck welding as was seen in some uncoated bullets . Photo NW2 .
Conclusion . Moly disulphide does help reduce neck welding in ammunition that is stored for a long time. However the tests were not sensitive enough to determine if the neck lube made things better or worse.
I have a suspicion only that it did help to some small degree.
However long term storage was not the aim of this test just the vehicle to see if Moly Mos2 does help at all in giving consistent neck tensions and reduce neck weld and from this test I conclude that it definitely does.
I am only talking about pure moly disulfide MOs2 coating done at home with a good quality layer of moly. No other coating or system.

I think the stress put on the case neck by seating a bullet is a key factor in the neck becoming harder over time and shrinking in diameter.
Linked to stress corrosion.

 

[308isgreat]

Re: Neck Tension vs. Time

As long as the change in neck tension does not affect your accuracy, don't sweat it. Most of my rifles don't care, but my 6PPC does. Groups will open up with it if I load the ammo too far in advance of shooting.