Neck tension and max bullet grip force

[ScottB338]

Does anyone know how much spring back tension is possible with any given neck diameter and/or case wall thickness for holding a bullet? Brass will stretch at a certain point and no longer provide an increase in the spring back force that would increase bullet tension.
At some point, I would think, further reducing the ID of the case neck will no longer produce increases in bullet grip force.

If, say, for example, has it been determined that a neck ID that is .005" undersize diameter of a
bullet, can only provide .002" of actual neck grip because part of that additional diameter reduction is lost to the brass yielding beyond spring back when the bullet is seated?

In this example, is the neck being tighter than .005" (or some other amount) under bullet diameter, just overworking the brass when the bullet is seated with no increase in bullet grip force due to the fact that the brass is pushed past its yield point?

Just wondering if anyone knows where the point of no return is.

 

[MagnumManiac]

It is understood that the amount of grip is only about .001"-.0015" once the bullet is seated, no matter how small you make the neck. The condition of the brass also has an affect, hard brass resists spring back and stretching, this may result in harder seating forces but the brass itself won't be holding the brass any tighter.
It is thought that bullet tension increases over time, hence why bullet weld occurs, but lubing the necks with graphite eliminates this.
Brass under tension over time can become brittle, known as age cracking and a few other names.
It's not just one size fits all when it comes to neck tension...actually resistance fitting.

Cheers.

 

[Wedgy]

Dissimilar metals can react and switch electrons and eventually "weld" to one another. Galvanic corrosion, electrolyic corrosion, electrolysis are other terms for it. There are many factors that come in to play with neck tension. If you have ever used an ultrasonic cleaner for you brass the bullets almost have to have lube on them, they actually squeaked going in and used way too much seating force, so I don't do that anymore. There is a point of no more tension but it depends on so many other things, mainly the brass.

 

[19 Badger]

I think neck thickness would play into this as well. Thicker brass(Lapua) that may be around .015" would have a little more tension than a thinner necked brand of brass of about .013". I said I think.... lol

 

[ShtrRdy]

Hopefully mikecr will see this thread and comment on the relationships.

 

[Mikecr]

You're right. Thicker brass can provide considerably more tension (and tension variance).
I suspect .308 circumference necks produce a flatter stress-strain curve than .224 necks, and that this would offset a greater area of gripping by some proportion.
We have shoulder angles resisting expansion, and 40deg shoulders would aid necks in resisting expansion more so than 12deg shoulders.
We have slightly different cartridge brass alloys, and of course variances in work hardness produced with our sizing plans.

With this, ultimately, we need a tool to measure neck tension. Not hardness,, not seating forces,, but actual hoop stress per use dimension.
If it was simple though, somebody would have done it.
I don't think we'll see it..

 

[Rhovee]

I can say for 100 percent fact that reguardless of spring back, there is a huge difference when shooting groups with .002 NT or .005. This is being measured from outside neck before seating bullets. Certain guns like more. Certain like less.

 

[ShtrRdy]

You're right. Thicker brass can provide considerably more tension (and tension variance).
I suspect .308 circumference necks produce a flatter stress-strain curve than .224 necks, and that this would offset a greater area of gripping by some proportion.
We have shoulder angles resisting expansion, and 40deg shoulders would aid necks in resisting expansion more so than 12deg shoulders.
We have slightly different cartridge brass alloys, and of course variances in work hardness produced with our sizing plans.

With this, ultimately, we need a tool to measure neck tension. Not hardness,, not seating forces,, but actual hoop stress per use dimension.
If it was simple though, somebody would have done it.
I don't think we'll see it..

Doesn't the friction between the brass and bullet affect the way a bullet is released, along with the pressure applied from the neck tension?

 

[ButterBean]

I can say for 100 percent fact that reguardless of spring back, there is a huge difference when shooting groups with .002 NT or .005. This is being measured from outside neck before seating bullets. Certain guns like more. Certain like less.

X-2

 

[ScottB338]

Like ShtrRdy says...
"Doesn't the friction between the brass and bullet affect the way a bullet is released, along with the pressure applied from the neck tension?"
It would be interesting to hear opinions on what happens first in those milliseconds at bullet release? ...is the bullet actually moving forward with the neck providing tension or is the case starting to expand and "change" the friction value between the bullet and case neck, possibly even releasing it before movement occurs?

 

[243winxb]

https://www.thehighroad.org/index.php?media/neck-tension-vs-bullet-pull.2235/full

and https://www.thehighroad.org/index.php?media/45-acp-necktension.476/full

i have not seen a test after the ammo was loaded for a longer period of time.
Does a 50 pound bullet pull , get less over time or more from cold welding?

 

[nealm66]

https://www.thehighroad.org/index.php?media/neck-tension-vs-bullet-pull.2235/full

and https://www.thehighroad.org/index.php?media/45-acp-necktension.476/full

i have not seen a test after the ammo was loaded for a longer period of time.
Does a 50 pound bullet pull , get less over time or more from cold welding?

More from my experience. I believe weatherby calibers benefit from tighter neck tension. I've also heard it can prevent secondary pressure spikes

 

[Rhovee]

I use an in-line Arbor press for all bullet seating. Seating force does not mean neck tension. There is plenty of ways to get light seating force with heavy neck tension. Powder graphite, nylon brush necks only, NeoLube etc. The trend I have seen is, the bigger the caliber the less neck tension shoots best. Only exception to the rule is the 300 wsm. Annealed with .005 NT shoots awesome.

 

[Mikecr]

#1 Interference fit is not tension.
Think about it for a second: tension is a force, if you could measure it, what unit of measure would result?
Would it be in inches or pounds?

#2 Seating force/friction does not directly correlate with tension, if at all.
You can lap bullets and neck IDs to dry white metal finish, observe very high seating forces because of this, and yet you will see zero affect of this action to load or MV.
You can coat bullets and Neck IDs in WS2 (tungsten) which holds the lowest dry film friction coefficient, observe very low seating forces because of this, and still see zero affect to load or MV.

#3 Bullets are neither pulled nor pushed from necks on firing.
The seating force test described at #2 debunks this notion as well.
Also, JFYI, pull force is usually higher than seating force -for less than mythical reasons.

Reality: Bullets are gripped by springback force against (X) area of seated bearing.
The gripping force is pounds per square inch.
Change LENGTH of neck sizing, given same seated bullet bearing, same interference, and same friction.
Observe that this does affect MV. In fact, it's a direct adjustment.