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Neck tension in general

Following up on another thread "how to measure neck tension", I wanted to go past apparent consensus that use of 'neck tension' as a misnomer is appropriate. It's just my belief that fallacies should not be perpetuated.

To begin, neck tension is not interference fit, nor represented directly(often no correlation) by seating/pull forces.
Another misunderstanding about the action of tension is seen with those believing we need a measure of 'pull force'.
Neither seating force nor the same as pull force hold's direct meaning about tension. These terms amount to no more than friction. You can affect seating friction many ways with no affect to MV at all. Yet you can measure the affect of an actual tension change with 1/16" change of length in neck sizing. This is because bullets are not pushed out of necks by pressure. They are released by necks expanding under pressure(even if only ~.0000001 over cal).
Bullet release is a matter of overcoming grip -not friction.
So what is grip?

The grip on your bullets amounts to spring back of the brass for the area applied(against seated bullet bearing).
Spring back of necks is typically 1thou for normal hardness, up to 2thou for extremely hard/brittle brass. That's it, and it's plenty enough. Normal spring back against .250" length of bullet bearing will provide more tension than against .125" of bearing. This is your partial neck sizing adjustment of tension. Grip of a given length is different for 22cal than 30cal.
With FL sizing of necks you can get more tension, a lot more tension, all the way to extreme and dangerous(depending on donut & seated bearing). This presents the potential to size length greater than seated bearing, and this extra length influences spring back that actually is against bearing. But other than achieving greater tension, I see more bad than good in FL sizing of necks, especially w/regard to tension variance. If you size way past seated bearing length, including donut area, well you've dramatically increased tension AND tension variance. Fine(and often desired) for a tiny 6PPC,, bad for a 7WSM.

So when a point blank BR shooter insists that 4thou under cal(interference) is magic with his 6PPC or 30BR, you need to understand that your LR cartridge is not a 6PPC, and that running typical ~75Kpsi+ competitive 6PPC pressures is not viable for you. He was probably FL neck sizing. While YOU'RE partial neck sizing, 4thou under is nothing more than overworking of necks anyway.
Try this:
Measure a neck OD as smoking from your chamber. Way undersize the neck for no more than seated bearing length. Let's say 5thou under cal. Seat a bullet, noticing the additional effort needed. Then pull that bullet and again measure the neck OD. You'll find that your seated bullet expansion sized the neck(which is bad), and that the neck sprung back ~1thou under cal. That is your tension(hoop tension, grip). It will do the same whether you size down 1thou or 10thou.
The only time this changes(in a single sizing action) is when you had sized beyond the length that the seated bullet bearing was able to reach/re-expand.

As far as measuring tension, there is currently no tool on the market to do this. If there were it would work something like a hydraulic expander inserted in a neck, which is between a v-block & indicator. We would turn up the pressure to expand the neck ~1thou and take a reading in PSI. When we released the pressure the neck would fully spring back(unless over annealed).
Seating force measure, if friction managed carefully, can provide a comparative measure that indirectly corresponds to tension variance, but we've been assigning too much credit to this IMO.
Frequent process annealing often increases seating force/friction but reduces actual tension. Not a bad thing if your load likes low tension, and lower tension also means lower variance of it. That doesn't mean it's best for everyone.

I'm a partial neck sizer(Wilson), and use bushings to achieve 1thou under cal after spring back and pre-expansion with a mandrel. Tension for me, even as a relative unknown in quantity, is useful, in that I can tweak tune with it -as sizing length. You don't here anyone talking about that, but there it is..

I'm not out to attack our notions, but to help with understanding about tension itself.
 
Again, I have tension gages, none of my tension gages are calibrated to 'tensions'. My tension gages are calibrated to pounds. Bullet hold, I want all the bullet hold I can get, I know, for years reloaders have pretended they understood neck tension, I know there are reloaders that insist all other reloaders agree with them. Then there are those that insist on renaming 'it'. The last 'new phrase' I read was 'hoop stress'. Again, I do not have a stress gage for measuring the hoop.

I want all the bullet hold I can get, I do not want my bullets to move until it is time.

F. Guffey
 
R. Lee covered this somewhat in his book. He stated that anything over .003" of "neck tension" was a waste as the bullet merely acted as an expander when it was seated.

Good post.
 
R. Lee covered this somewhat in his book. He stated that anything over .003" of "neck tension" was a waste as the bullet merely acted as an expander when it was seated.

He also included factors.

F. Guffey
 
RE: MIKECR
"This is because bullets are not pushed out of necks by pressure. They are released by necks expanding under pressure(even if only ~.0000001 over cal". Where do you get you information from? VarmintAl states that the necks do not expand from pressure releasing the bullet.

"This is because bullets are not pushed out of necks by pressure". If it is not pressure moving the bullet forward what force do you think it is? This doesn't make sense.
 
I know,, if said bullet has a jump of say .020" the neck would expand and let pressured gases around the bullet before bullet plugs into the lands and bore.

I'd have to say a load with light neck tension,, the primer alone pops the bullet into the throat first.

Just my 2 cent
 
Daniel.308 said:
I know,, if said bullet has a jump of say .020" the neck would expand and let pressured gases around the bullet before bullet plugs into the lands and bore.

I'd have to say a load with light neck tension,, the primer alone pops the bullet into the throat first.

Just my 2 cent

I posted the question about pressure blowing out the neck while the bullet was still in the neck about a year ago. VarmintAl answered my post and answered the question and said it doesn't expand the neck while the bullet was in the neck. I cannot remember how he came to that conclusion. Cannot find his comments with a search, also not on his website. When the bullet engages the rifling I would think a lot of the bearing surface was still in the neck. Gas couldn't get around the bullet. If the neck is blown out when the bullet is still in the neck then annealing and tension wouldn't accomplish anything? Inside neck texture and lube would have no influence if the neck expands and no longer touches the bullet. Sometimes I feel these discussions are too wandering and no solid facts. I judge whether something is helpful by looking at the target. People can post all kinds of measurements and theories. If one person could post dead on factual answers you wouldn't need 50-100 replies.
 
Neck tension in the short range point blank so to speak BR shooting
The desire for more neck tension with the predominantly thin necks of .0082 really came about with the use of compressed loads of N133 that would push the bullet out causing inconsistent seating depths.
Some have went away from the standard .262 NK to a .268 NK looking for more grip to run theses full cases of powder.

That has been my only experience regarding neck tension and accuracy. Without enough and compressed loads can turn into inconsistent seating depths which is IMO one of the worst things to hurt accuracy

I have experimented with a wide range of neck tension without any noticeable change on the target with the exception of the sernario I have stated above.
 
A fact is that I always have carbon on the outside of necks on my reloads, no matter what caliber, brand of brass or neck tension . I just wish my necks would expand enough to stop the carbon from getting there. I've annealed ran up over max pressure, every thing in 5 barrels.

So in my theory and fact, the shoulder seals the pressure since I do not see any carbon there at all.
 
I always surmised that the lower the effort needed to get the bullet moving, the greater would be the degree that carbon smudge left down the neck.
 
JohnKielly said:
I always surmised that the lower the effort needed to get the bullet moving, the greater would be the degree that carbon smudge left down the neck.
That is why I believe more tension can tune some bullet and seating depths. I believe it has to-do with the chamber sealing and more consistent velocities. I also believe it is easier to see at longer ranges. Matt
 
The softest thing in the chamber is the bullet...wouldn't it deform first and seal the chamber at the neck/shoulder junction? Great topic
 
I'm with Matt and Webster on this, At 1000 yards you can see a difference between a tight neck and a loose one! So that tells me you have more pressure because the neck has a tighter grip on the bullet and therefore it holds the bullet in place longer while building pressure. So I belive this is a factual answer!

Joe Salt
 
Joe Salt said:
I'm with Matt and Webster on this, At 1000 yards you can see a difference between a tight neck and a loose one! So that tells me you have more pressure because the neck has a tighter grip on the bullet and therefore it holds the bullet in place longer while building pressure. So I belive this is a factual answer!

Joe Salt

I agree with that because I've seen it myself. For instance my 6br loaded with light neck tension shot right on the money at 28 MOA at 1000 yards. Brand new Lapua brass with significant neck tension put me right over the target. They both grouped the very well at 100 yards and 1000 yards though, well for me anyway about MOA at 1000 with no flags shooting off the top of my van.LOL
 
The thing about pressure pushing vs. the neck expanding is it is being taken here as an absolute one or the other. The question is why it could not be a combination of the two. Certainly it does not take a huge amount of pressure to move a bullet as if that was the case, none of use would ever be able to pull bullets from a loaded round. I would guess that the initial movement is pressure pushing and depending on how fast the bullet move out, pressure could also be involved in neck expanding.
 
amlevin said:
R. Lee covered this somewhat in his book. He stated that anything over .003" of "neck tension" was a waste as the bullet merely acted as an expander when it was seated.

Good post.

Before you believe that BS you better test. I have, many of us run .004" or more with our dashers. Why? Tests PROVE accuracy impromentments at 1k. All that matters with neck tensions is that its consistent and you test to see how much the gun likes.
 
I am wondering if any of you folks are getting carbon or powder residue on the necks of your case's?

This is a good thread and am not saying anyone is wrong here,, just trying to learn.
At a match I witnessed a guy who didn't have powder in one of his cases. He didn't know it but it was primed. The primer ignited and you could here it pop, so he went to open the bolt and to pulled back stiff at first then came open. The bullet was into the lands a little not much and we had to tap it out with cleaning rod from the muzzle end. I asked him if he was jamming his load and he said "no".

I watched Tony Boyer clean the outside of his necks right after he fire his record shots, and I know he is usually a jammer and use's a good amount of neck tension.
 
Daniel I run my necks with about 3 thou. clearance, so yes I get carbon down to the shoulder. But I also size the whole neck. Some guys may only do half or even three quarters so the brass may seal faster doing that. Then you should only get carbon part way down the neck. There are probably more variables like with just neck sizing.

Joe Salt
 
zfastmalibu said:
amlevin said:
R. Lee covered this somewhat in his book. He stated that anything over .003" of "neck tension" was a waste as the bullet merely acted as an expander when it was seated.

Good post.

Before you believe that BS you better test. I have, many of us run .004" or more with our dashers. Why? Tests PROVE accuracy impromentments at 1k. All that matters with neck tensions is that its consistent and you test to see how much the gun likes.
I agree. For short range BR, a .256 bushing for a .262 neck chamber (.260 loaded round) with a full case of N-133 is magic (depending on temp. and humidity> N-133's downfall).
 
jlow said:
The thing about pressure pushing vs. the neck expanding is it is being taken here as an absolute one or the other. The question is why it could not be a combination of the two. Certainly it does not take a huge amount of pressure to move a bullet as if that was the case, none of use would ever be able to pull bullets from a loaded round. I would guess that the initial movement is pressure pushing and depending on how fast the bullet move out, pressure could also be involved in neck expanding.

I agree, it is not hard to imagine a simultaneous bullet movement and neck expansion. Certainly pressures high enough to Ka-Boom a receiver if completely contained are strong enough to move a bullet through any amount of neck tension AND expand the neck at some point in the process.
 

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