Neck tension - looking at it the wrong way?

[Webster]

Most of what I have read on neck tension refers to the diameter of the sized brass to create and interference fit with the bullet. The idea is, the tighter it is, the more force required to push the bullet. The AMP seating press is advertised to tell you how much pressure it takes to seat your bullet, inferring that similar seating pressure should result in similar dislodging pressure.

Are we looking at neck tension the wrong way? What I mean by that is, at least the way I understand the explanation, is that it's function of friction between the bullet and the case.

However, during the firing process (per Whelen Vol. 2 pg. 4), it doesn't work quite like that. As the pressure in the case builds, the bullet is not pushed forward with a tight neck. On the contrary, as pressure in the case builds, it expands the neck freeing the bullet to then move forward.

So my questions are, if bullet movement is dependent on pressure and neck expansion, is measuring interference fit and seating pressure the correct approach? I would think the plasticity/ductility (not sure which is correct term) of the brass neck would play a role. Or, is interference fit a close enough measurement that a handloader can measure, so that is why it is used?

Of course, "neck tension" as it applies to interference fit does play a role with bullet movement before firing like in magazine jostling, loading a round in chamber, etc.

Townsend Whelen 1877-1961. He was 60 years old in 1937. He had no means to determine that pressure expanded a case neck around the bearing surface before the bullet moved forward. It had to be his personal opinion. Whelen and Powley did a lot for our sport but they lived in a different time era. Top SR bench shooters will tell you that neck tension has an affect on accuracy, but most of use will never see the difference because we cannot shoot aggregates around 0.220". If your concerned about it do what the big boys do and feel confident you have taken care of tension properly.

An Eric Cortina video about annealing then sizing and running a mandrel in each neck showed scattered bullet seating force when measured with a pressure guage.

Like others said let the targets show you if it makes a difference. Ignore the hundreds of personal opinions.

 

[Bc'z]

Years ago, I tested this starting with a well tuned load for my 6PPC. The load was shooting really well in a .262 chamber. Since I had the bushings with me, I backed up to .001 neck tension, and the group went to hell. Nest I tried .002 and it got better, but was still not as good as it had been at .003. This sort of thing is so easy to test that it makes me wonder about all those who seem to prefer conjecture to what is such an easy test. I should add that 133 likes neck tension. These days I might be using .004. Other powders do not share this characteristic. In a PPC, LT32 seems to like less. .0015 to .002 would be fine.

I don't know enough to give definitive explanation but I'm a believer that powder has a huge part in the equation.
My experience loading 123gr bullets for a 6.5cm with IMR4166, initial testest charge/seating was with a .288 bushing.
Looking to see if there would be an improvement with bushing adjustment It wound up shooting the smallest with a .286 bushing.
Moving forward I thought I'd try some SWP all case prep sizing and bullet was same, only change was powder...
It didn't pierce the primer it blew it clean out of the brass. Well the pocket was expanded enough when ejected I had to go fishing for the primer.
This unpleasant experience gave me a pretty solid conclusion that some powders like more while others like less.
Weather the cartridge involved or barrel configuration plays a role I don't know, I just don't have the experience to say.

 

[gunsandgunsmithing]

I know that others see differences but honestly, I seldom see changes from neck tension. Since I'm blessed to have a couple of boringly accurate mid teen rifles and another that's not far behind them.. and have been at the br game for a while, I don't feel like it's due to not being able to shoot the difference but that my guns and loads are less sensitive to neck tension changes than some. We're not just talking a couple of guns but several and many, many barrels and countless thousands of rounds. Since I don't doubt what I hear from others that I respect in this game, I have to conclude there is a reason for both conditions and can only surmise that it is likely due to jamming the bullet to varying degrees almost always with my loads. I have a range at my shop and I test just about everything and pretty extensively. Even a lot of off the wall stuff sometimes deserves testing but certainly, when a lot of top shooters claim something as gospel..I absolutely test those things a lot. Often, I find things to work but often, just the opposite. There are few absolutes in this game is all I can say.

I do think that jamming logically plays a role here. It's also logical that while the neck expands before the bullet gets far, that it may well start, stop and start again, when jumping.

Nevertheless, if the neck indeed opens first, I have a hard time reconciling in my little brain how neck turning and small inconsistencies matter a lot on target. I went to full on no turn necks in 2019 and I have not regretted it for an instant, so far. This is even on brass that has been necked down considerably. I used to swear by neck turning and considered it a must but the targets are telling me a different story and I really like not needing to do that job.

 

[mikecr]

I should add that 133 likes neck tension. These days I might be using .004.

It's just a shame that we can't measure neck tension to see it on a stress-strain curve.
My thinking centers on neck elasticity.
Necks recover (spring back) around 1/2thou to 3/4thou depending on hardness.
If you move beyond that, the brass does not fully recover, it yields (sizes).

Any stress-strain curve I've seen shows diminished gain in tension while exceeding recovery stress.
That's not a problem where not concerned about hardening, and it could be beneficial for sure.
No problem.

Tension would still be expressed correctly in PSI. Not in bushing sizes or interference fit.
Your tension is still tied to spring back force, and the area that force is applied.
I think that's what this thread is about.

 

[lotech]

Ultimately, comsistent group sizes tell you how important or unimportant neck tension is, just like ES and SD numbers.

 

[CharlieNC]

I know that others see differences but honestly, I seldom see changes from neck tension. Since I'm blessed to have a couple of boringly accurate mid teen rifles and another that's not far behind them.. and have been at the br game for a while, I don't feel like it's due to not being able to shoot the difference but that my guns and loads are less sensitive to neck tension changes than some. We're not just talking a couple of guns but several and many, many barrels and countless thousands of rounds. Since I don't doubt what I hear from others that I respect in this game, I have to conclude there is a reason for both conditions and can only surmise that it is likely due to jamming the bullet to varying degrees almost always with my loads. I have a range at my shop and I test just about everything and pretty extensively. Even a lot of off the wall stuff sometimes deserves testing but certainly, when a lot of top shooters claim something as gospel..I absolutely test those things a lot. Often, I find things to work but often, just the opposite. There are few absolutes in this game is all I can say.

I do think that jamming logically plays a role here. It's also logical that while the neck expands before the bullet gets far, that it may well start, stop and start again, when jumping.

Nevertheless, if the neck indeed opens first, I have a hard time reconciling in my little brain how neck turning and small inconsistencies matter a lot on target. I went to full on no turn necks in 2019 and I have not regretted it for an instant, so far. This is even on brass that has been necked down considerably. I used to swear by neck turning and considered it a must but the targets are telling me a different story and I really like not needing to do that job.

I expect there are so many of these "depends on" factors as you mention, that explains many of the disagreements concerning results. Everyone says you must test everything for yourself, which is contrary to the state of worldwide scientific knowledge about everything we take for granted in our lives. But outside of the military our shooting is only a hobby without an organized approach for proper learning and collective knowledge. And I'm really enjoying 22LR!

 

[mikecr]

What I'm getting at is that neck tension can be adjusted through area of sizing (length) rather than bushing size. You could go with reasonable interference, and around half seated bearing length of sizing from a bushing, rough develop your load, and then tweak sizing length. Dial right into what your load likes, instead trial & error with different bushings.

You can also do this with a hunting capacity cartridge instead of messing with an in-the-land (ITL) relationship.

 

[gunsandgunsmithing]

What I'm getting at is that neck tension can be adjusted through area of sizing (length) rather than bushing size. You could go with reasonable interference, and around half bearing length of sizing from a bushing, rough develop your load, and then tweak sizing length. Dial right into what your load likes, instead trial & error with different bushings.

Isn't that assuming the bullet moves before the neck opens?

It may but the thread I mentioned earlier from brc involved a guy I have a lot of respect for as being a sharp cookie. His name is Keith Sharpe, and engineer and professor at UofL. He stated simply that the lighter object moves first. Kinda hard to disagree with that when you think about it.

I can see pressure or tension being greater than the mass of the neck too. So if we say that's the case, jamming seems to change all the rules due to the force then needed to get the bullet moving. At the least, it would seem to make bullet movement very much more consistent than jumping, relying on tension/pressure alone. FWIW, this logic is the reason I jam most everything.

 

[BoydAllen]

It's just a shame that we can't measure neck tension to see it on a stress-strain curve.
My thinking centers on neck elasticity.
Necks recover (spring back) around 1/2thou to 3/4thou depending on hardness.
If you move beyond that, the brass does not fully recover, it yields (sizes).

Any stress-strain curve I've seen shows diminished gain in tension while exceeding recovery stress.
That's not a problem where not concerned about hardening, and it could be beneficial for sure.
No problem.

Tension would still be expressed correctly in PSI. Not in bushing sizes or interference fit.
Your tension is still tied to spring back force, and the area that force is applied.
I think that's what this thread is about.

View attachment 1492615View attachment 1492618View attachment 1492619

The relevance of this information, depends on how you have visualized the problem, for example, just behind the heel of a FB bullet, or at the transition to a BT, the neck of the case that it is seated in is the as sized ID. A step of sorts is created at that point, which, depending on its size is likely to increase the force required to seat the bullet deeper in the case. This can increase the amount that a bullet can be seated into the rifling without being pushed back. It has been my experience that the depth to which bullets are seated into the lands affects tune. None of this is reflected in the graphs you have provided, which is not to say that the information is incorrect. It does suggest that the problem is more complex than it might seem to be, which is why I continue to believe that the best way to evaluate this stuff is by careful testing, and looking at the resultant targets.

 

[AlNyhus]

What I'm getting at is that neck tension can be adjusted through area of sizing (length) rather than bushing size. You could go with reasonable interference, and around half bearing length of sizing from a bushing, rough develop your load, and then tweak sizing length. Dial right into what your load likes, instead trial & error with different bushings.

I used to think that too until Stan Ware and I developed the .30 WolfPup that has an .085 neck length. It responds to neck bushing changes just like conventional neck length .30's (30BR, 30x47 etc). -Al

 

[mikecr]

Yeah Boyd, if your neck sizing length exceeds seated bearing, you will get base-bearing junction binding.
This, significantly increasing tension (and variance of it). That's not something I want.

 

[mikecr]

I used to think that too until Stan Ware and I developed the .30 WolfPup that has an .085 neck length. It responds to neck bushing changes just like conventional neck length .30's (30BR, 30x47 etc). -Al

You're talking about an extreme, with very small length adjustment available. Right?
A portion of it's tension is coming from the shoulder, and a bushing there is merely extending the shoulder.

 

[BoydAllen]

Yeah Boyd, if your neck sizing length exceeds seated bearing, you will get base-bearing junction binding.
This, significantly increasing tension (and variance of it). That's not something I want.

Long standing conventional benchrest wisdom suggests the opposite. In my experience, and that of others you do not want to feel the pressure ring of a bullet getting past the sized part of the neck as you seat the bullet. Again, IMO this is best evaluated by shooting and examining targets.

 

[VA_XTC_Shooter]

It's just a shame that we can't measure neck tension to see it on a stress-strain curve.
My thinking centers on neck elasticity.
Necks recover (spring back) around 1/2thou to 3/4thou depending on hardness.
If you move beyond that, the brass does not fully recover, it yields (sizes).

Any stress-strain curve I've seen shows diminished gain in tension while exceeding recovery stress.
That's not a problem where not concerned about hardening, and it could be beneficial for sure.
No problem.

Tension would still be expressed correctly in PSI. Not in bushing sizes or interference fit.
Your tension is still tied to spring back force, and the area that force is applied.
I think that's what this thread is about.

View attachment 1492615View attachment 1492618View attachment 1492619

Yes, you understand what I'm trying to say. Thanks!

 

[Webster]

It's just a shame that we can't measure neck tension to see it on a stress-strain curve.
My thinking centers on neck elasticity.
Necks recover (spring back) around 1/2thou to 3/4thou depending on hardness.
If you move beyond that, the brass does not fully recover, it yields (sizes).

Any stress-strain curve I've seen shows diminished gain in tension while exceeding recovery stress.
That's not a problem where not concerned about hardening, and it could be beneficial for sure.
No problem.

Tension would still be expressed correctly in PSI. Not in bushing sizes or interference fit.
Your tension is still tied to spring back force, and the area that force is applied.
I think that's what this thread is about.

View attachment 1492615View attachment 1492618View attachment 1492619

If pressure expanded the case neck before the bullet moved then there is no neck tension against the bullet. It's called hoop tension. There are formulas on internet for calculating hoop stress but they don't include the materials properties. Since we cannot calculate hoop stress we measure change in diameter which has nothing to do with hoop stress. So we size to a certain diameter then size smaller our bigger and look at the results on the target. Sizing the same way should give you close to the same hoop stress even if you don't know what the actual stress value is.

 

[Alex Wheeler]

Im not so sure the carbon on the neck happens early in bullet travel. Id think its more likely to happen as the bullet is farther down the barrel and pressures drop. I run a lot of neck tension without annealing in many cases. I dont run super tight necks. So the neck has the most clearance of any other part of the case. Soot on the necks has never bothered me

 

[mikecr]

All true Webster. I'm only trying to get folks to acknowledge that tension IS NOT interference fit.
This understanding could be useful because there can be different approaches to our adjustment of tension, for the goal of starting pressure.

Nothing is free, so every option should be considered -with understanding beyond [I tried this, it shot better or worse].. You know there is always more to that.

 

[Alex Wheeler]

The issue with adjusting length is that you dont want to push the pressure ring all the way through the sized part of the neck. If you do then you have no more control over neck tension. The pressure ring just expanded the neck on the way through. When you seat them that deep you will feel the bullet pop through and seating gets real easy once that p-ring has cleared the sized part of the neck. Adjusting neck tension with how much sized length would only work if your combination likes very light neck tension and you r playing on that end of things. Most stuff in my experience likes a lot of neck tension. Far past the yield of the neck.

 

[mikecr]

Im not so sure the carbon on the neck happens early in bullet travel. Id think its more likely to happen as the bullet is farther down the barrel and pressures drop.

Tight chamber end and neck clearance stops sooting completely.
If you don't want to go that way, you can trim a case another 10thou shorter and watch sooting go up.

What happens is that some of the gas passing around the bullet initially finds the easiest path as around the case mouth along all that clearance, while the bullet is in a tighter throat (than neck), still engraving.
The gas is just going everywhere it can in an order of least resistance.
The carbon in that gas has mass. At chamber end the mass would have to take a 180 to soot necks and build up where case mouths snap to seal. Obviously that happens, but it is more difficult with a tight chamber end clearance. Less room to make that turn.
Tighter neck clearance allows necks to seal faster, providing less of a run for gas/carbon.

 

[gunsandgunsmithing]

Apparently the question has been answered to some and I missed it...the bullet moves before the case opens. Or so it would seem. Maybe it's opened for long, heavy bullets but not yet for the short and stubbies, or with a long freebore.

IDK, so I'm asking and would like a better understanding too. If it's open, neck tension, by whatever term, should not affect tune. If not, then yes, especially if jumping. I would conclude from that single statement, jamming is a good thing. Again, I'm asking. I think we must first conclude if the neck is open or not..or somewhere in between, before we can go forward with this subject but that's just my 2 cents and worth less,, probably.