Neck tension

ShtrRdy said:

If you change neck interference, (tension), do you need to re-tune the load to see if it made a difference?

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If I'm changing neck tension it is part of load tuning.

Testing neck tension is pretty straight forward.......Once you have done your powder charge/seating depth test... load up some rounds at .002-.004-.006 neck tension it will show what a particular load prefers.

wasskeet said:

Brent, others - could you post what each component measurement is to arrive at a given neck tension?
Ex:
loaded round = X
bushing used = X
mandrel (if used) = X
etc.

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On the back end I don't bother with any of that. Pin gauge and done. Will measure to the closest 0.0005" if not closest 0.0001" depending on which pin tolerance you buy. There are tolerances with everything you mentioned - neck thickness, bullet diameter, even the mandrel unless you verify it with a mic (but that's a one and done). That's not even getting into run out and lack of concentricity.

If the case before loading passes the correct pin gauge and doesn't pass the next one up, doesn't matter, all those tolerances get averaged out IMO.

@wasskeet on my 284 Win-Imp I use a .313" bushing, then a .282 Mandrel a loaded round measures .316

wasskeet said:

Brent, others - could you post what each component measurement is to arrive at a given neck tension?
Ex:
loaded round = X
bushing used = X
mandrel (if used) = X
etc.

Click to expand...

Example
Loaded .2935-.294- non neck turned brass
Bushing .291
Mandrel .292

BrentM said:

Do any of you play with it or set it and tweak the loads? One of my rifles seems to really like .004-.005. Test load shown.View attachment 552727 It got me side tracked because I usually target .002ish and leave it for all rifles.

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I've never tried it but I'm sure it makes a difference.

Ive read that any neck tension over .002" doesn't add any more tension.

Tighter ES/SD seems to occur more with a higher tension or interference, from the little I've tried. The .003-.004 compared to .002
Maybe getting a more uniform ignition or uniform burn sooner in the barrel?
I'm using freshly annealed brass each loading.
The arbor press "gauge" shows the seating pressure, makes it easy to see the consistency.
Not all my guns have a Wilson seater, some are still done the regular way.

Same with others, I use a mandrel and set to about .002 for bolt guns.

For ARs however, go with .004. The force of the bolt cycling in a these type of stroke are rather violent, and it keeps my bullet from moving any during that process.

Even using NATO ammo, like in the military, I've had bullets get pushed into the case, every now and again.

Koda_ said:

Ive read that any neck tension over .002" doesn't add any more tension.

Case Neck Tension - A Stress Analysis

Neck Tension and Case Hardness

bisonballistics.com

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Kinda of odd don't ya think? I mean just pressing a bullet into a sized neck you feel the difference quite easily. It's really not much different than a hose or pipe fitting. Clamping force is directly related.

BrentM said:

Kinda of odd don't ya think? I mean just pressing a bullet into a sized neck you feel the difference quite easily.

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I'm no engineer but the article made sense to me, though I'm not certain if a blanket .002"NT apply to all situations. I dont know if I could feel the difference between .002 and .004

How much does hoop strength change with hardness of said brass?
You could have super hard brass or super soft brass and the interference the same at .004", but which brass is getting more tension?
I will leave this for you all to ponder…
Also, brass does not release bullets as it slips out the neck, the neck expands first, and inertia moves the bullet a few milliseconds later after all tension is lost…

Cheers.

You can find out real quick how much neck tension amount is by pressing the seated bullet tip into the bench or something. A non charged or primer'd one would be smart.
If you want to know the scientific numbers, then add weight by five lb increments until the bullet moves. I'm sure we all have a comparator.

If you have that much spare time, then do it for every manufacturers brass, virgin, FL resized, annealed etc.

Maybe pull 20 bullets of each and see which is more the pita..

dfanonymous said:

You can find out real quick how much neck tension amount is by pressing the seated bullet tip into the bench or something. A non charged or primer'd one would be smart.
If you want to know the scientific numbers, then add weight by five lb increments until the bullet moves. I'm sure we all have a comparator.

If you have that much spare time, then do it for every manufacturers brass, virgin, FL resized, annealed etc.

Maybe pull 20 bullets of each and see which is more the pita..

Click to expand...

This is the problem, pounds required to seat bullets has nothing to do with bullet release. It solely is force required to overcome the expansion of the neck, nothing more, the brass neck is not putting that much force on the bullet, not measured in weight anyway, only in resistance.
If we take the militaries specs, their ammunition MUST have a minimum resistance pull of 30lbs…is that the resistance from the neck gripping the bullet or the crimp they so often use? Not to mention the sealant they often use too…

Bullet release is very different to bullet seating force. Once the neck has expanded by the bullet, it's true only job is to keep the bullet from falling out during transportation and handling…

Cheers.