Neck wall thickness vs neck tension

[Shinbone]

Just wondering if anyone has noticed any kind of relationship between neck wall thickness and neck tension, and accuracy? Of course, it is all about what your rifle likes, but has anyone noticed a general relationship between the first two and the third?

Since measuring actual bullet-gripping force exerted by the neck is not easy without a bullet seating force measurement capability, most people gauge gripping force by the interference fit between loaded and unloaded neck diameter and call that "neck tension", i.e. "neck tension is .002" means seating the bullet expanded the neck diameter by .002."

However, such talk ignores neck wall thickness' (NWT) contribution to bullet-gripping force. Intuition says NWT should also have a big influence on the actual gripping force on the bullet exerted by the neck. In other words, the thicker the neck wall, the more gripping force there is for a given interference fit. However, I never see anyone say ".002" neck tension with a NWT of .015." It seems discussions focusing on interference fit only, which is the predominant way of discussion neck tension, are ignoring half of the equation.

Why discuss neck tension without including NWT?

 

[3Sigma]

My guess is that it is more about consistency in thickness.

.002" interference fit on a diameter(.306) on a .308 bullet will yield the brass if it is 1/2 hard or softer.

Less interference pushes into the specifics of that lot of brass, its metallurgy and conditioning (work hardening, annealing/stress relief, times fired, etc.), more interference won't change the grip pressure much as it will only spring back a partial amount.

This spring back amount is the "grip", and I doubt thickness makes much difference in the numbers we would be considering (.004" or less). Annealed, times fired, and sizing operations will likely impact this more.

But that is all theoretical as I have never studied it. Just an engineering analysis.

Edited for spelling errors

 

[gunsandgunsmithing]

Just wondering if anyone has noticed any kind of relationship between neck wall thickness and neck tension, and accuracy? Of course, it is all about what your rifle likes, but has anyone noticed a general relationship between the first two and the third?

Since measuring actual bullet gripping force exerted by the neck is not easy without a bullet seating force measurement capability, most people gauge gripping force by the interference fit between loaded and unloaded neck diameter and call that "neck tension", i.e. "neck tension is .002" means seating the bullet expanded the neck diameter by .002."

However, such talk ignores neck wall thickness' (NWT) contribution to bullet gripping force. Intuition says NWT should also have a big influence on the actual gripping force on the bullet exerted by the neck. In other words, the thicker the neck wall, the more gripping force there is for a given interference fit. However, I never see anyone say ".002" neck tension with a NWT of .015." It seems discussions focusing on interference fit only, which is the predominant way of discussion neck tension, are ignoring half of the equation.

Why discuss neck tension without including NWT?

Your point is valid but it all boils down to what your gun likes and internet data is best viewed as just a reference. Same with seating depth... We get all up in arms about how to determine a precise number that's only relative for internet discussion and ultimately, we still have to do our own load workup. If we all had seating force gauges, we could all have exactly the same numbers but some guns will still like more or less....but we'd all be speaking in the same language, which is not always so in your point about neck thickness' effect on tension.

 

[Straightshooter1]

Just wondering if anyone has noticed any kind of relationship between neck wall thickness and neck tension, and accuracy? Of course, it is all about what your rifle likes, but has anyone noticed a general relationship between the first two and the third?

Since measuring actual bullet gripping force exerted by the neck is not easy without a bullet seating force measurement capability, most people gauge gripping force by the interference fit between loaded and unloaded neck diameter and call that "neck tension", i.e. "neck tension is .002" means seating the bullet expanded the neck diameter by .002."

However, such talk ignores neck wall thickness' (NWT) contribution to bullet gripping force. Intuition says NWT should also have a big influence on the actual gripping force on the bullet exerted by the neck. In other words, the thicker the neck wall, the more gripping force there is for a given interference fit. However, I never see anyone say ".002" neck tension with a NWT of .015." It seems discussions focusing on interference fit only, which is the predominant way of discussion neck tension, are ignoring half of the equation.

Why discuss neck tension without including NWT?

Not only the thickness, but also the diameter of the neck. Different diameters for a given "neck tension" of say .002 will be different.

It's all about which works best in you're particular chamber, and of course, the most important thing is that it's all consistent.

 

[GetReal]

My guess is that it is more about consistency in thickness.

^ ^ ^

If the neck wall has inconsitent thickness, a bushing alone isn't gonna get ya consistent neck tension.

I'm not saying ppl who use bushings alone never shoot far better than I do.

But since I don't turn the neck, to get consistent OD's, I use a mandrel to get consistent ID's

This produces consistent neck tension.

 

[3Sigma]

^ ^ ^

If the neck wall has inconsitent thickness, a bushing alone isn't gonna get ya consistent neck tension.

I'm not saying ppl who use bushings alone never shoot far better than I do.

But since I don't turn the neck, to get consistent OD's, I use a mandrel to get consistent ID's

This produces consistent neck tension.

For my setup, I use a bushing that is smaller than desired then mandrel up to target. I've found that unannealed brass with 3 or 4 firing and resizes needs a little more encouragement to resize, requiring a smaller ID bushing.

My next step was to start annealing (or stress relieving), but my process is pretty redneck and not ideal (torch and socket with Tempilaq).

 

[GetReal]

For my setup, I use a bushing that is smaller than desired then mandrel up to target. I've found that unannealed brass with 3 or 4 firing and resizes needs a little more encouragement to resize, requiring a smaller ID bushing.

My next step was to start annealing (or stress relieving), but my process is pretty redneck and not ideal (torch and socket with Tempilaq).

Same here. Tho on Petersons recommendation, I start annealing after the second firing.

 

[3Sigma]

Same here. Tho on Petersons recommendation, I start annealing after the second firing.

I had to learn the hard way (no pun intended) on lapua 22-250 brass. Now it is like yours... fire form, shoot one more time, then anneal after every shot from that point forward.

 

[GetReal]

BTW, I'm one of them hi- faluting self righteous, holier than thou AMP annealers.

(In truth, I don't trust myself to get it right on my own. )

 

[markm87]

BTW, I'm one of them hi- faluting self righteous, holier than thou AMP annealers.

(In truth, I don't trust myself to get it right on my own. )

I anneal every time because I can go directly from SS media tumble and use annealing for drying the brass (after a rinse)

I found that even hand annealing, for me, beats NOT annealing as far as neck tension consistency. I know a nice annealing system could do more consistent work, but hand annealing gets me some real gains.

 

[Shinbone]

Thanks for all the replies. Some folks make some pretty good points about it being more about consistency than actual neck tensions value, etc.

Some people "tune" neck tension as part of their load workup process. So, I personally think it is more than just being consistent. Those that do tune neck-tension pretty much all do it by using different neck bushings to get different interference fits. How come we never hear about tuning by trimming neck wall thickness?

BTW, there's already tons of threads on annealing, and no doubt that annealing affects neck tension. It'd be great if we could keep this thread focused on the relationship between neck wall thickness and neck tension since it hardly ever gets discussed.

 

[3Sigma]

I guess my comment was more that it is a second or third order variable, way down on the pareto.

 

[markm87]

I use the K&M arbor press for seating. It has the gauge option, but I don't have the gauge.

The press gives a pretty good feel on seating neck tension, and I can't say that I've ever notices neck thickness giving me noticeable variances in seating pressure/neck tension.

 

[Shinbone]

I use the K&M arbor press for seating. It has the gauge option, but I don't have the gauge.

The press gives a pretty good feel on seating neck tension, and I can't say that I've ever notices neck thickness giving me noticeable variances in seating pressure/neck tension.

(emphasis mine)

I think that is a very interesting result.

 

[Dave M.]

The OP is correct in his thought process though. Inner diameter and wall thickness are both key components when calculating Hoop Stress (which includes the “T” that we all call neck tension). Regardless of annealing and the yielding of material, .015” neck wall thickness with .002” of interference will NOT result in the same tension as .010” wall thickness brass with a .002” interference fit. This is not speculation, this is pure engineering fact. I’ve never thought about it the way the OP put it, but I’ll often talk to folks about “neck tension” with complete disregard to brass wall thickness, and technically this is wrong. Thanks for getting me to look deeper at it. Good luck.
Dave

 

[Dave M.]

^ ^ ^

If the neck wall has inconsitent thickness, a bushing alone isn't gonna get ya consistent neck tension.

I'm not saying ppl who use bushings alone never shoot far better than I do.

But since I don't turn the neck, to get consistent OD's, I use a mandrel to get consistent ID's

This produces consistent neck tension.

Damn it….I loved everything you said, right up until the point where you said you use mandrels. I guess we’ll have to be arch mandrel enemies from now on….LOL.

 

[Dave M.]

I anneal every time because I can go directly from SS media tumble and use annealing for drying the brass (after a rinse)

I found that even hand annealing, for me, beats NOT annealing as far as neck tension consistency. I know a nice annealing system could do more consistent work, but hand annealing gets me some real gains.

NOOOOO….not tumbling with SS pins. This is hurting your accuracy. Trust me.

 

[mikecr]

As Straightshooter1 mentioned, thickness and caliber affect tension (bullet grip).
Tension is springback force against a given area of seated bullet bearing. Sizing length against seated bearing affects grip area as does the circumference. Thickness and hardness affect springback force.
Higher thickness and higher set tension in general means higher variance of tension.
Extremes in tension either high or low may affect your ability to hit on a good load with chosen powder.

There is no reason to even try to compare one person's supposed tension to another, as there is currently no way to measure neck tension. The information is hopelessly uncorrelated.

 

[GetReal]

Damn it….I loved everything you said, right up until the point where you said you use mandrels. I guess we’ll have to be arch mandrel enemies from now on….LOL.

You and your anti - mandrel fettish.... what did mandrels ever do to you?

 

[JFrank]

Additional reading material

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...

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