Neck Tension Debate

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Shane Tuttle

Staff
I peruse through a couple of reloading pages on Facebook time to time. My question comes from a couple of guys arguing neck tension, there. So, consider that source for what you will.

Someone was in the middle of working up a load on a rifle cartridge for target. I believe he was working at 300 or so yards with the ultimate goal of dialing in at 1000yds. Started with COAL, a known good powder/bullet/case/primer brands for his cartridge, etc. to get a good baseline. His rifle was grouping quite well after figuring the right powder load and bullet leade. Looked like it was just under 3" at 300yds. Another poster piped up and said powder charge isn't that important as long as you're under max load. But neck tension is key for the tightest groupings. Everything else is secondary. The debate went downhill from there.

So, if that's true, why is that? I can see having sound concentric case necks and consistent neck tension would make a difference to a certain degree. But this guy was talking about it making a bigger difference in tight groups than powder charge and COAL. My mind is thinking; how is a couple of pounds difference in tension relevant to tens of thousands of psi generated when firing?

What am I missing, here?
 
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nhyrum

New member
Well. First of all, I think neck tension, correct load, and correct jump are all important.

But, let me play devil's advocate. When working up a load, often a velocity and/or poi shift plateau are found and the middle node used. Basically, that means you've got, usually, +/-.3 grains of wiggle room on the load and have it not really affect your velocity or point of impact.

Bullet jump is similar. You've got a window that the bullet likes (I believe berger says there's generally a . 06 "window") that the bullets generally like. So again, you find the window your combo likes and set it on the shorter end of jump(long on the oal) so as the barrel erodes, you stay in the window.

So, getting and keeping an EXACT powder load and jump, is really not that important.

Neck tension, I feel like, doesn't really have a window, or has a very narrow window that is preferred. But, I feel neck tension is easy to set, there's really no chasing needed, it's pretty well known that .002 is pretty much perfect, give or take .001 and it's a set it and forget it for deal



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Shane Tuttle

Staff
That's what my line of thinking was: set it and forget it.

He was saying a couple thousandths difference would make a major change in point of impact. I don't get that.
 
4

44 AMP

Staff
What am I missing, here?
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One thing you're missing is how some people get focused on the esoteric minutae of target reloading. And how some folks will steadfastly defend their pet theories to the death, no matter the evidence or lack there of...

Look at it in more general terms. Once you have determined the precise combination of factors that your rifle shoots best, then it is consistency that creates accuracy. Uniformity = consistency and that = accuracy.

Consistency of EVERYTHING. All the factors, in the ammo, and the gun, AND the shooter.

Another poster piped up and said powder charge isn't that important as long as you're under max load.
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This might make some sense in context but other wise its a load of crap. Tiny variations in powder charge weight normally won't make a difference, but larger ones certainly will.

Suppose your "perfect" load charge is 48.0gr, rounds with 47.9 or 48.1gr won't make much (if any) difference in your group size. Now suppose every 3rd round only had 45gr in it. THAT WILL make a difference, I'd be willing to bet cash on that.

Yes, I love shooting holes in overbroad blanket statements, especially when its so easy to do...:rolleyes:

Things like "ideal" amount of" ...whatever. Might be the ideal for that guy and his gun, is it going to be for you and your gun??? Maybe, but there's no guarantee.

Find what works best, for you, with your gun and ammo components and loading practices. What someone else does may be a useful guideline, or may not, but its not holy writ, even if they think it is.
 
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nhyrum

New member
I haven't really played around with it. I do feel like that smaller changes in neck tension will have more a difference than small changes in charge weight, and slightly more than jump

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nhyrum

New member
reddog81 said:
How exactly do you measure neck tension and then how do you adjust if it's not the "correct" amount?
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Neck/Bushing diameter - 2x brass thickness at the neck -bullet diameter.

You adjust neck tension really in one way, and that is by changing the size of your neck Bushing. You can turn down the thickness of the neck, but that's mostly to uniform the thickness of the neck, and all the necks

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reddog81

New member
nhyrum said:
Neck/Bushing diameter - 2x brass thickness at the neck -bullet diameter.
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Not trying to argue but is that really a measure of neck tension? Those are the factors that create neck tension. I would expect some thing like 10 ft lbs of force or something similar.

It's like asking how much pressure is a load creating and someone answering 4 grains of powder... the 4 grains of powder creates the pressure but it's not really a measurement of pressure.
 
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nhyrum

New member
Neck tension is a measure of how much smaller the neck opening is than the bullet. I agree with your point though that it's not really measuring tension

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Jim Watson

New member
Not trying to argue but is that really a measure of neck tension? Those are the factors that create neck tension. I would expect some thing like 10 ft lbs of force or something similar.
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Right. In fact there are mil-specs on "bullet pull" but I don't know of a consumer device to measure it. I think there is a press die that measures the seating force but it is not common.
 
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hounddawg

New member
Just a couple of random thoughts on neck tension

easiest way to determine what yours is take a sized case, seat a bullet, measure the neck OD. Pull the bullet remeasure. That will show you how much spring back you are getting. To go a step farther measure the neck before the seating, that will show you how much of the deformation is plastic and how much is elastic. It is the elastic part that is the neck tension.. Try this on several cases and if the numbers differ you might want to think about annealing

On the subject of how much, I always use .003. That is the number that Litz came up with as the best all around in his Modern Advancements Vol II. The BR boys say that number is fluid, might be .001 on one rifle, might be .004 on another rifle.

I do know that unannealed cases with random numbers of firings will cause those random what the heck flyers that ruin groups. Either anneal all the time or none of the time and keep cases on the same number of firings

anyway just my thoughts on the matter, may or may not be 100% accurate or apply to everyone
 
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hounddawg

New member
I think there is a press die that measures the seating force but it is not common.
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The AMP press

those hydraulic press's are a joke. The more pressure you put on the pump handle the higher the gage reads . You would need a constant pressure constant flow accumulator set up to get any relevant data


Scroll through F Class John's Youtube videos for videos of the AMP Electronic press plus a whole bunch of other great videos on long range precision shooting
 
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Bart B.

New member
The correct term for this issue is bullet pull or push force. It varies with the amount of interference fit and neck brass hardness and wall thickness.

How many pounds of force is needed to push the bullet out of the case neck

If a 30 caliber bullet needs 10 pounds of force to get it out of the case neck, that happens when the case has about 130 psi in it.

Examples....

30 caliber military ball ammo specs, 60 pounds minimum.

30 caliber military match ammo specs, at least 20 pounds.

30 caliber handloads for competition, sometimes less than 5 pounds.
 
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hounddawg

New member
The correct term for this issue is bullet pull or push force. It varies with the amount of interference fit and neck brass hardness.

How many pounds of force is needed to push the bullet out of the case neck
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It is a common misconception that soft equals elastic. In fact steel and brass springs are made with some of the hardest steel and brass available. Ask any knife or blademaker about using old automobile leaf springs to make blades. Both the elasticity and the hardness of a substance is bot determined by the molecular structure of the metal but for different reasons and one does not determine the other.

on your second sentence you are ignoring surface friction which could be altered by adhesion, or lubrication that would affect pull/push force and would be independent of any elastic properties of the neck

https://www.nanoscience.com/techniques/mechanical-testing/mechanical-properties/

Elastic Modulus

The elastic modulus (E), often referred to as Young’s modulus is the ratio of stress (σ) to strain (ε) when deformation is totally elastic. In the elastic region, stress and strain are proportional through Hooke’s Law: σ = Eε

The elastic modulus is an intrinsic property of a material. At a fundamental level, E is a measure of the bond strength between atoms. The greater the modulus, the stiffer the material and the smaller the strain. An elastic response is non-permanent, so when an applied load is released, the sample returns to its original shape.



Hardness
Hardness (H) is a measure of a material’s resistance to deformation by surface indentation. The plastic deformation is caused by the motion of dislocations in the atomic structure of a material. The yield strength of a material may be changed by inhibiting dislocation motion through imperfections, alloys or grain boundaries.

Material hardness can be increased by different means, including interstitial or substitutional hardening, where atoms are either added between or substituted in the atomic lattice:
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Unclenick

Staff
If you put a strain gauge and strain gauge amplifier on your press you can measure either seating or pulling force, but it is some bother.

Referring to the measurement of interference fit between bullet and neck as "tension" is a long-used and widely accepted but misappropriated handloading term. Tension is the stress you apply by pulling something taught or elongating it. The difference in diameters of the neck before and after bullet pulling is actually a measure of the interference fit between the neck and the bullet. That said, when the neck is expanded by the bullet, that grows its circumference, so you are applying tensile hoop stress to the neck that is tension. Because of that effort, there is radial compressive stress on the bullet. So, while "tension" not a technically precise way of describing the bullet situation, there is bullet hold brought about by compressive radial stress that results from the tensile hoop stress from stretching the neck that is related to how hard that bullet pull is. That number, in turn, is modified by specifics like the coefficient of friction between the brass and gilding metal and the surface finish.

The difference this makes to accuracy is that higher bullet pull tends to help produce more consistent ignition and barrel time. There are two or three milliseconds between when the primer ignites and the powder's burn starts building additional pressure. Because the priming mix has a relatively high brisance, its pressure presents almost immediately upon ignition, and should that primer pressure start moving the bullet during the short delay while the powder gets burning, it changes the effective volume in which the powder's pressure develops, contributing to variation in pressure and velocity and barrel time. A commonly complained of example of this problem is in the 22 Hornet. With its small case with a thin neck, it famously shoots unsatisfactorily with many standard primers, but starts doing much better with a switch to the mild Remington 6½ or with pistol primers.
 
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