Neck tension and max bullet grip force

[ShtrRdy]

It's ok to use a dry film lubricant in new necks. Other than moly, it won't change anything over a fired carbon layer, and won't affect MV.
Do not use a wet lube..
Moly does affect MV (lowers it), but this is NOT due to reduced friction. Moly is special in that it cools the charge with it's phase change.
A latent heat of vaporization, that other dry films do not introduce.

I recently did an experiment where I used Redding Dry Neck lube before seating bullets versus not using any lube before seating bullets. The brass was twice fired Lapua brass. Everything else was the same. The cartridges that used Redding Dry Neck lube were higher velocity than the ones without.

 

[Hoppsing55]

https://bisonballistics.com/articles/case-neck-tension-a-stress-analysis

Interesting article related to the topic discussion.

 

[Muddyboots]

These are the threads to go to 4 fingers in glass.

 

[Mikecr]

I've run tests between WS2 coated bullets and bare. No change in MV for me.
WS2 is pretty much the slipperiest dry film in existence.
So I can't explain difference MVs some have seen with dry lubes.

Doesn't make sense -on the surface. But I'm sure it makes sense somehow with all conditions examined.

 

[nealm66]

I wonder if freebore and jump come into play might explain some difference

 

[Old Rooster]

Baboltin good question and others have influenced me positively towards Mandrel's and neck lube.
My velocities have not changed enough to attribute the change to neck lube but my results may not be as well run as others and I check my velocities with a Chrony and not a better Chronograph.
I use dry neck lube and have been brushing the lube out after using my mandrel but I was told that could induce bullet weld so from this point on I will let the graphite stay in the neck to resist bullet weld.
Old Rooster

 

[Baboltin]

Baboltin good question and others have influenced me positively towards Mandrel's and neck lube.
My velocities have not changed enough to attribute the change to neck lube but my results may not be as well run as others and I check my velocities with a Chrony and not a better Chronograph.
I use dry neck lube and have been brushing the lube out after using my mandrel but I was told that could induce bullet weld so from this point on I will let the graphite stay in the neck to resist bullet weld.
Old Rooster

How will you let the graphite stay just by not ultra sonic cleaning the brass ?

 

[Old Rooster]

Cleaning my brass comes right after de-priming.I use a universal Lee de-priming die so I won't get powder residue in my Redding dies.They de-prime many different caliber cases.
I then size my brass and put them back into vibrating case cleaner to get a final polish removing all marks the sizing die left.
After my brass comes out of the vibrating brass cleaner with corn cob media I then I prime cases and then use the mandrel dipped cases into the dry neck lube to set my neck tension.
Using a mandrel is last step before powder and bullet seating so I always am putting powder into clean cases.
Just my routine and others may do it differently.
I have been reloading since 1967 but used a hand reloader back then and in 1973 I bought my first press a RCBS Partner press.
It would be interesting to hear the reloading routine others use.
Old Rooster

 

[longestrange]

Anyway, while seating, that brass rolls outward and curves back onto the bullet bearing. It is a very slightly bowed grip. The greater the sizing, the greater the bowing energy added. If friction were normalized between, a 2nd seating(without that upsizing) would be way easier, but trust me on this: tension is still the same.
With either the 1st or 2nd seated bullets, having a slightly bowed grip, if you run a pull test the force can be higher than would be expected as the bow is taken out. It's a Chinese finger trap effect. It's not always what you have, but it does explain differences seen in past pull tests.

Having difficulty visualizing what you are saying. Are you saying the case mouth flares out or crimps in as the bullets are seated?

 

[Mikecr]

Having difficulty visualizing what you are saying. Are you saying the case mouth flares out or crimps in as the bullets are seated?

A flaring/recovery curve just behind the sizing point. An extruding phenomena.
Excerpt from published in Precision Shooting, 2009, James Boatright: Yielding of Brass Case Walls in the Chamber:
----------------------------------------------------------------------------------------------------------------------------------
When compared with actual measurements, calculated bullet seating forces seem to be running too large by a factor of about
two to three. I can identify two of the possible geometric, mechanical effects that are ignored in this simple "radial expansion" analysis,
but that would cause us to calculate significantly smaller bullet seating forces if they could be included.
The largest effect being ignored could be termed the "transition cone" effect.
As the bullet is being seated into the case neck, it pushes a traveling "pseudocone" of neck wall material ahead of its base.
The cone angle in the vicinity of the leading edge of the base of the bullet would increase disproportionately as larger
amounts of neck expansion are attempted.
After being swaged up, the brass material in this area tends to "overshoot" the actual bullet diameter because it needs to re-bend
into a cylindrical shape once again. The tensile stress stored in the case neck is reduced by this effect throughout the "expanded cylinder"
portion of the enlarged neck when compared to the simple radial expansion calculated.
In fact, this reduction in neck tension and in bullet seating force builds up so significantly with increasing neck expansions that it
becomes dominant and accounts for the relative maximum in neck tension that we find at about 1.5 to 2.0 mils of neck expansion.
The other significant effect being ignored can be called the "Chinese finger-trap" effect.
This "friction multiplier" effect comes about whenever we attempt to slide a thin-walled sleeve upon a mandrel having a
slight interference fit inside that sleeve. If we push the sleeve from the rear (as we are doing here in bullet seating),
both the normal force of the sleeve upon the mandrel and its resulting internal friction force are significantly reduced. [An axially
compressed, short, thin-walled cylinder will tend to assume the familiar "barrel shape" as it enlarges in diameter with each of its two ends constrained from freely expanding.]
However, if we were to pull the sleeve along by its front edge (as would happen during"bullet pulling"), the friction force on the mandrel
inside the sleeve would be greatly increased by the converse of this same effect. Hence, we have the familiar "bamboo," or
"Chinese," "finger-trap" mechanism that we utilize in woven wire to enhance the "grip" of cable-end pulling devices.
------------------------------------------------------------------------------------------------------------------------------------

This is an intelligent person considering calculated -vs- observed seating forces and stress/strain (tension).
It's been done many times over past decades,, always demonstrating IMO that there is more to it than can be consolidated to simple.
So, it seems ludicrous that folks simply coin interference fit, and seating friction, as 'tension', while they are clearly three separate things that do not directly correspond.
Bottom line: We need a tool to directly measure neck tension, and to know what our bullet release preconditions actually are.

 

[Reloader222]

After almost 30 years of reloading I have killed another culprit which cause flyers - Neck Tension. After resizing without the ball expander in die, I run all cases through a mandrel to ensure that neck tension is the same. I regularly anneal necks. After sonic cleaning brass to get rid of most carbon on the brass, I tumble them in my Lyman Case Tumbler to polish the brass.

 

[longestrange]

People tend to interpret stress/strain curves incorrectly. For annealed brass, you see the 'stress' go up at the modulus until the material yields, then gradually increase, then gradually decrease until failure. The actual stress, however, is increasing because the area decreases. If you unload a tensile bar before failure, it will come back up to the maximum previous load before yielding again. That would be called 'work hardening'.

 

[Mikecr]

Work hardening, or 'stress hardening'. The grain structure(which I see as character) changes as we go past the point of yield.
It changes every time we go there, so I try to minimize it. Otherwise, I would be locked into constant annealing.

 

[GLTaylor]

OK, I'm on to another post. You guys outran my headlights about 2 counties ago........