Neck Tension

[Mikecr]

I don't know if harder brass springs back with more or less distance.
It may react differently with phases of hardness, and 30cal necks could spring more than 22cal necks.
Dead soft (over annealed) has no life and will not spring back. Extreme hard (over worked) resists dimensional changes with high forces, but I don't know that it actually springs back more (could also be less).

Then you have brass no longer new and taken to yield region (sized up or down). It will not spring back to original, and it seems more inclined to go back where it had yielded to. This is demonstrated with brass fired in high clearance chambers, losing enough spring back to extract reliably, even with heavy sizing.

IMO, brass either left at or springing to a dimension, in itself, would not indicate it's spring back force potential.

 

[wjm1000]

One thing I noticed in this post is that no one mentioned the difference in the brass hardness. One or two post mentioned annealing to make all cases equal. But for those that don't do it every time I've found there is a significant difference in the hardness of the brass from one piece to the next. I don't care how you resize your cases the harder case will have more spring-back than a softer piece and have different neck tension. You can usually feel this when you seat the bullet. I made a taper gauge with a very shallow taper and separate my cases accordingly. All cases must be the same overall length before using the gauge. If you do the math you can measure in millionths of an inch.

 

[Matt F]

You guys might be interested in this article:
https://www.ampannealing.com/articles/55/annealing-under-the-microscope/

New bullet seating press with a load cell and motor to drive the seating ram.
The software allows the seating pressures of each round to be saved so that they can be compared to the next reloading cycle. This way it can track how the neck tension progresses with each load.

 

[Mikecr]

If you keep drinking the kool-aid, you will end up hopelessly separated from truths..
I see endorsement of FULL annealing. It's implied (as though a great condition) in the 'study', declaring that their "correctly annealed cases" for the test have no spring back at all. They're dead. They also disclaim accuracy results here as it's dismissed from the actual endeavor.
I don't know if they really believe that's what we want or not (they seem to). But to sell us on that, they continually set up conditions to demonstrate how consistent dead brass is..

Yes, dead cases have little to no spring back,, and yes that will vary little.
I'll even concede that this would be great provided your load performs well with dead brass. But you know what? New Lapua brass is not killed with full annealing. It comes to you in a process annealed condition, which is merely stress relieved. New Lapua brass does spring back outward from bushing sizing without expansion(a little). Same with shoulder bumping. It has life in it. This is normal, and what most of us are managing.

Seating force and pre-seating force measure has been around a long time. Even systems with similar software. What all of you need to understand for yourselves, is that seating force is very heavily tied to friction and not a direct measure of tension. It is useful, if no more than a comparative sense, to detect tension changes -provided you tightly control friction(normalizing it).
Also, go ahead and consider interference fit as meaningless to actual tension.
Just try it, and think about it on your own.
I could describe simple tests you can do yourself to see it. An adage this would lead you to is "Truths pass all tests". But I invite you to think & stop blindly following mass sentiments, or worse, merchandising.

 

[MagnumManiac]

Am I correct that within .001 of a second, the neck expands, all tension is lost and the bullet starts it's path into the rifling?
For a minute amount of time in the burn, the bullet is held in place, even longer if it has received a crimp.
Then the neck loses all 'grip' on the bullet.

I never believed the neck lost grip that early in the burn, but even firing a primed only case with a bullet seated into it in a different cal rifle shows the neck has lost tension on the bullet afterwards.
I fired several primed only 264WM rounds through my 338WM rifle.
The bullets actually fly a considerable distance with a magnum primer.
After firing these, the bullet would easily fall into the neck.

So, how soon is the neck expanded and the bullet freely moves?

I really would like to know the answer to this.

Cheers.

 

[Mikecr]

The scales of this internal ballistic process are extreme.
Very small, very fast, very sensitive.

Beginning with powder;
If you load a shell case with primer/powder and no bullet, on firing you get WOMF.
Fold a piece of paper and gently set it on top of the powder column,, on firing you get BOOM. With any real initial confinement you get POW.
Confinement leads to pressure, and pressure speeds the powder burn. All powders are variable in burn rate, and potentially to either end of burn rate charts.

On releasing of a bullet;
With partial neck sizing no further than seated bullet bearing, and a bullet in place, the neck OD is cal + neck thickness. Necks are not 'squeezing' bullets, but resting against bullet diameter with only their spring back force. How far would a neck in this common scenario have to expand to freely release a bullet? REALITY: Difficult to measure with an electron microscope. Perhaps billionths of an inch.
When folks claim you need ~2-3thou of neck clearance to be safe,, that's as likely analogous to 2-3ft on scale..
How much pressure would the primer/powder need to exert against the entire area of a case to expand a neck ~0.000000001"? I don't know, maybe 10psi depending on the case area and angles,, it ain't much. A folded piece of paper resting on the powder column would immediately jack the pressure this much. Engraving force is a little higher, so a bullet will not go far on primer firing alone, but it would be fully released here and travel for a moment.
If this process suddenly relied on overcoming bullet seating friction (pull force), primer firing would not move a bullet, and every gun in existence would explode on it's next firing with current powder loads..

Scenario #2; You FL size necks to leave something like 3thou interference.
Everything about this is excess, and causing extreme starting pressures, with extreme variances of that. Now you likely have a sized length of neck behind & smaller than seated bullet bearing. This, binding the base-bearing junction with forces including neck hardness, donut thickness, and shoulder angle. Such a neck would have to expand way way more (~2thou) before releasing a bullet. This is actually beyond expansion to outright upsizing.
Unless running an unerbore that relies on extreme starting forces, don't FL size necks. And you might as well stop downsizing necks so much that you're just re-upsizing them with bullet seating. This is not what bullets are for.

Crimping is unique. The neck would expand to release the bullet, but the bullet is still held back by the crimp(for a short period). In this case I'm sure the bullet has to overcome both the force and a friction of that crimp, or be held until the neck has upsized to clear the crimp from bearing. That's where you really need neck clearance.
I imagine the ballistic results would be similar to FL sized necks.

 

[tdot]

Hey MikeCR,

Just outta curiosity, what is your background? Are speaking of all this stuff from a perspective that you work in an industry that actually studies all of these theories? Or are you simply hypothesizing and throwing these out as facts?

Not trying to be a dick, genuinely curious. Some of ideas make intuitive sense, some do not.

 

[Mikecr]

If you're reaching for authority, I'm not it.
I'm only hoping you'll consider it, test it, understand it. Trying to help

 

[tdot]

Definitely not reaching for Authority and don't need help thinking outside the box (as you'd mentioned earlier). I just like to know what people are basing their purported knowledge on. I know of a few Flat Earth Fanatics who are quite convinced the world is flat, they also believe they are smarter then the herd, because they think differently. Doesnt make them right, or smart. But then again, when Columbus sailed from Europe 500 years ago, everyone was pretty convinced he was going to sail off the edge of the earth. So it's all a matter of perspective.

 

[tdot]

But at the end of the day, this thread is about neck tension. While I agree that the terminology may be incorrect we are not technically measuring tension, when we measure the OD change of the brass.

What I will suggest is that using our commonly available tools, measuring the change in OD is one of our best ways to repeatedly replicate the force that is applied to the bullet. Testing should be done by each individual to find what works best for them and their loading process to obtain repeatable results in their gun, with their ammo in their conditions. It is up to the user whether they can consistently repeat that loading process and therefore replicate their results.

And while people may not specifically speak of brass density, neck thickness, the coefficient of friction of the interior of the neck, the coefficient of friction of the bullet, or any of the other possible variables. If all of the potential variables are repeated and consistent, then the "neck tension" can be inferred from the change in the "neck diameter".

If we all really wanted to get pedantic, then we could also talk about the fact that a .264 neck has a tighter arc then a .375 neck or even a .30 neck. Therefore there is inherently more strength to that arc and more resistance to deformation. (Think bridge building, and also the arc of a leaf spring). And there are many more examples of the minutiae that we could discuss.

All things that we can't readily measure.

So for now I'll continue to measure neck OD and replicate my loads based on that. Whether it actually measures tension or not, it is repeatable, and that is the important part to me. And likely the reason that the herd uses the method.

If someone can come up with a better mouse trap, then I'm all ears.

PS. No disrespect intended, though I think I might be borderline.

 

[bigedp51]

For all of you with Lee sizing dies just forget everything you have read so far in this posting and settle for the neck tension or bullet grip that your die gives you.

And those of you with RCBS sizing dies you might want to polish your expander and remember to lube the inside of the case necks.

The rest of you need to get a grip.