Monitoring Neck Tension in ft-lbs as opposed to neck size

[ELR LVR]

One thing we should all also consider....
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The neck expands to release the bullet, so neck tension may be a Non-sequitur....within bullet release

Now whether neck expansion happens immediately upon primer pop
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Or whether case pressure must build up enough first and the bullet has had to move against neck tension
That I don't know....
has anyone set a camera up inside the case and chamber to know this???

 

[ELR LVR]

I ran a quick and ugly experiment for you's guys
I first looked at my press and measured some linkage ratios to try and get a rough idea for the combined leverage when seating a bullet
I roughly guesstimated a 15:1 ratio, although knew that once the press neared the top and the linkage and began to cam over it developed much more multiplied leverage near the top of the stroke.
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So I remembered I have a spring weight gauge
And set a 22BR case on the bottom anvil and pressed a bullet into the neck
The force weight showed 45 lbs before starting to insert the bullet into the case
and developed up to 50 lbs of pressure required to continue to seat the bullet down into the neck.
I kept going past where the so called donut may be to see if pressure rose any...
.....It did not
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This was one of the cases that I mentioned took 1 pound of Reloading press ram arm force
to seat the bullet
and in actuality corresponded to a required 50 lbs of vertical force to do so.
I knew it was past 20 lbs becuase you cannot pull a bullet with your fingers which if it was 1 lb of vertical force would easily be pulled with fingers.
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Hope this gives you all an idea of whats going on, EVEN WITH light neck tension

 

[mikecr]

Neck friction (seating force) is different than tension.
Tension is neck spring back force against some area of seated bearing (PSI).
There is no method on the market to measure neck tension.

 

[Webster]

I, like just about everyone else, approach neck tension based on how much i am resizing the neck using a combination of neck sizing bushing and a mandrel. I also use a K&M Arbor Press with Dial gauge when seating my bullets. I typically use the gauge just to monitor seating consistency. When preparing for a match, i will separate my loads based on seating resistance derived from the dial gauge.

I did an experiment with my 6.5 creedmoor whereby i confirmed some (very slight) resistance when sizing my neck with the mandrel and then slightly reduced the size of my CM case neck for some cases but still used the same mandrel in the neck. This test resulted in seeing a slightly higher pressure to seat my bullet.

After this test, i started paying more attention to the bullet seating resistance in terms of ft-lbs as opposed to neck size/mandrel. I also use this number to help me compare MV/SD/ES of different loads based on bullet seating resistance.

Just wondering if anyone else pays attention to ft-lbs of resistance when seating bullets.

My theory is that performance of slower burning powders can potentially benefit from tighter neck tension and am looking for real data to make that comparison as opposed to just relying on the bushing/mandrel size.

Look at Eric Corina's video with seating pressure results. With the best case prep the ft/lbs was all over the place.

 

[quest450]

I agree it's nice to have the data but, how does the data guide you when it comes time to pull the trigger?

Nice seating BTW

this program lets you sort loaded rounds by "peak pressure" or "work done" so I'm basically shooting my sighters and score rounds with almost identical neck tension / seating force, eliminating another variable, I wouldn't want to shoot my five rounds with neck tension/seating pressure varying by 30psi
At the end the Indian still has to pull the trigger.

 

[Webster]

Look at Eric Corina's video with seating pressure results. With the best case prep the ft/lbs was all over the place.

If you ignore some calculated tension, it's just friction resistance to movement which we cannot measure. We measure neck diameter change because we can and assume it gives the same friction of the bullet sliding against the neck. We still don't know if pressure expands the neck before the bullet is released. I don't know if seating force is the correct relationship to determine friction. Watching Erik Cortina measuring force to set a bullet, the bullet starts moving with a low ft/lb reading and increases as more bullet enters the neck. Friction is not measured in ft/lb units. Looks like neck tension is the best we can do. Make them all the same.

 

[mikecr]

We can normalize neck friction by allowing the carbon layer provided on firing, and cleaning or coating of bullets. We can monitor seating or pre-seating forces.
With pre-seating using a mandrel, forces can be adjusted to match -before seating bullets.
I do this through LENGTH of neck sizing.

I suggest that bullets are normally 'released' from necks, long before they would be pushed out.

 

[D-4297]

Here is a thought to mull over : Since almost ALL of our brass shows powder Blowback on the necks of our cases , yet we all want to have that "Case-seal" at the shoulder , that would indicate the bullet is released , and moving , long before we get case-shoulder expansion . Ergo ; neck tension is only applicable to how many milli-seconds neck pressure is held on the bullet . Physics would indicate that bullet release is virtually instantaneous .
Pressure ; like water , will seek the path of least resistance , even though it would be following the channel around the bullet diameter , and along the inner neck wall . It would take less pressure to move the case neck wall , than move the bullet forward .
This is all just thinking about possibilities in the process . Nothing more .

 

[mikecr]

Another thought: bullets are swinging in the wind with as little as ~0.000000001"(maybe half this) of neck expansion.
This occurs long before pressures would overcome neck/bullet friction, especially with larger cals.