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What is the purpose of neck tension?

S

SicVic

Sergeant of the Hide
Full Member
Minuteman
Mar 14, 2021
177
161
Michigan
#1
So I have my opinion and I load accordingly.
I talking about a bolt gun ( mine is 6.5 CM)
Please don't write a novel or attach a bunch of tutorial links; just a few quick highlights will do.
If you think it does 3 jobs then put them in order.
I would like to see what the prevailing thoughts are.
Again, I'm not asking to be taught just asking what you think it does.
 
#9
So I see we are beginning to hint around at grip (perv term) or amount of tension.
Acudaowner, if we can keep you conscious long enough to answer if the amount of tension matters...??? Aside from blacking out.
 
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#12
OREGUN said:
Holds the bullet.
Click to expand...

Screen Shot 2021-09-28 at 1.09.51 PM.png
 
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#13
You guys are good.
So I've posted this because I'm fishing for the general mindset of what tension does as I'm in the process of making another video on the subject.

Here's a scenario: Two test groups, same charge, same brass, same development. Everything is the "same" as you can get it.
One group seated at .003" tension or 45# press weight one has zero tension set into the case mouth by hand.
Now what happens since neck tension is the all deciding factor??
 
#16
spife7980 said:
Youre asking for a one dimensional answer to a many dimensional question.

If you did proper development on both then you wouldnt be loading them the "same"

So it depends.

And .003 isnt a measure of tension. Its a measure on interface fit. People just use terms incorrectly and it becomes slang.
Click to expand...
I like that.
The interface fit would provide a resistance that could then be measured as a way to replicate the action if one desired.
 
#17
SicVic said:
I like that.
The interface fit would provide a resistance that could then be measured as a way to replicate the action if one desired.
Click to expand...
Interference would provide one dimension. Its easy to measure that.
You didnt want links but you should read this link
1632860999355.png


All of that makes up bullet grip and its really really hard to measure outside of a lab. Numbers 6 and 9 are particularly hard to quantify your control of for consistency.
 
#19
Increased chamber pressure during the initial firing. Maybe thats too much, maybe its not. Depends on all the rest of the details of the load.

Maybe thats good for where your barrel and bullet like to be for optimal accuracy, maybe its not. Cant guarantee anything
 
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#20
It's looking for an absolute answer to a non-absolute problem. I have seen annealed brass blow apart (head case seperation) because the neck tension was ridiculously tight.
 
#21
spife7980 said:
Interference would provide one dimension. Its easy to measure that.
You didnt want links but you should read this link
View attachment 7711521

All of that makes up bullet grip and its really really hard to measure the actual bullet grip outside of a lab.
Click to expand...
You Sir are a facilitator of good information information and I appreciate that.
I'm after the ones who call out new reloaders and tell them "it has to be this way"
In reality, it pretty much stops at " it holds the bullet"
After that, situations dictate.
I'm here just to see how some process the importance and functionality of neck tension.
 
#24
spife7980 said:
You just want enough to be secure enough for your goals without disrupting the bullet jacket and core and making it off balance.
Click to expand...
This is really good. Let's say you expanded the mouth just to the point where you could seat a bullet with your fingers. Just enough tension so it doesn't fall down inside with the case standing upright.
I know you would have to insert it by hand as you're not stripping it otta the magazine but what would you expect from the results compared to the others that you seated the way you normally do?
 
#25
Way back when I initially started with my little lee hand loader that you used a mallet to neck size and seat the bullet with I noticed that some times when I would fire the next round in the magazine would have the bullet shoved all the way into the case. I had fired those poor reminton 3006 cases so many times to what was obviously just minums at best but over time the necks were thin and hard enough so that the little die didnt do enough sizing to be more than tangential contact, it wouldnt move from just touch but you could push it out. I would just pull the bullet back out to be in the neck to some little pressure and they never shot unsatisfactory to my standards. Obviously my standards were much more lax than they are now so I cant quantify it.
 
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#26
alfmoonspace said:
It's looking for an absolute answer to a non-absolute problem. I have seen annealed brass blow apart (head case seperation) because the neck tension was ridiculously tight.
Click to expand...
Alf, I think I can believe this could happen....
This is one of the examples I was looking for.
In short, neck tension increases pressure due to restricted force on the bullet.
I've also heard that tension aids in facilitating powder burn providing a improved bullet launch.
So we should see a pressure decrease if light tension is used?
 
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#28
Neck tension is as much the problem as the solution.
First, zero neck tension is not practical.
Those hotdogs that like to rip that bolt handle like it's a reciprocating saw blade would have their rig blown apart from a deep seater in under 5 seconds.
I like to test stuff and have the facilities to make it, walk it to the gun and shoot it.
I've been working with "no tension" seating. It's nothing new as Alf pointed out.
What's been interesting is how it dispels a lot of common beliefs.
Tension causes problems and not just at home...
Difficult to measure, tough to replicate, concentric issues, various questionable intell, Manufacturers bidding the next big toy. Quite a challenge.
I find that if I compare two exact test sets with jump set at touching lands, one with tension and the other without.
The zero tension set produces a lower SD, a better group, a slight velocity increase (avg 10 fps) and the same poi (after velocity difference adjustment)

Again, not practical but it does hold it's ground against those who say " it has to be this"
 
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#30
Alright, that's it for me.
Wife just texted so I gotta hurry up and act like I've been doing something productive.
Once I get the video edited I'll post it here.
Gotta give the haters some hate candy for Halloween.
Thanks to all for your thoughts.

Vic
 
#38
jeffpatton00 said:
Another factor is that insufficient neck tension can result in bullet movement due to recoil and other forces unique to semi-autos.
Click to expand...
Not unique to semi-autos, though. A heavy recoiling bolt gun can move an improperly tensioned bullet.

Very common when people load .303 for Enfield SMLE rifles using .308 bullets… when the Enfield uses .311-.312 bullets. No neck tension and the bullets pack up in the case… and no land engagement, so they can’t hit minute of deer at 50 yds.

Does neck tension matter? Yes. Should it keep you up at night… no. The primer
Alone will pop a bullet out of its case. The neck tension is a factor, but not a critical factor, in internal ballistics.

Sirhr
 
#39
I’ll second everything @spife7980 said

My noted goal/reasoning would be:

- Consistent round to round tension. Which contributes to consistent seating depth when you press the bullet in

- Enough tension to hold the round for your desired use.

*Some fclass guys soft seat a round. So it fully seats when it contacts the lands. Giving a “fresh” tension on each round (much like guys who seat them a bit off where they want them then fully seat them before a match.) Also ensures each round is just touching the lands

*Some bolt guys target .0015-.0030 to be consistent and hold the round under recoil/chambering from mags

*Semi Auto guys run heavier tension to keep from the round moving under the recoil of a carrier etc

-Some also run bushings/mandrels etc to keep from overworking or minimize the working on the neck of the brass. Tight chambers with minimal tension obviously work it the least. Sloppy chambers and heavy tension/crimps on semi guns are likely to work it the most. Which can shorten the brass life especially without annealing
 
#42
Just chiming in that when you set the jump at “touching lands” that will change some things.

The primary resistance is now always the lands. So generally speaking, you should see better results with less interference fit and/or friction (as it’s already been pointed, we were dealing with many factors in “neck tension”).

Once you back away from the lands. Then it’s going to change a bit. The entire spectrum of “neck tension” is going be in effect as the initial resistance upon primer strike is the “neck tension.”

Simple answer: find the amount of “neck tension” that doesn’t allow the bullet to move under the conditions you run the rifle in and also maintains a consistent release. Generally speaking, it’s a sliding scale. Change one thing and you’ll likely have to adjust another to maintain the consistency.
 
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#44
Scottfree92 said:
The very important fact is that this interface value must be able to be repeated time after time for any type of shot consistency
Click to expand...

So, I think we can/have vaguely defined what neck tension in. The interference fit between the bullet and case neck, also with regard to more obscure topics like “grab” (how grippy the interior of the neck is), “cold welding” (the interaction between two dissimilar metals), uniformity of neck wall thickness and it’s presence on the outside vs. inside of the neck, and elasticity of the neck (a factor of times fired/annealing regularity).

All of this is good and well... but how does a reloader enhance consistency across loads?

Cold Weld - Easy, either load close to the match, coat bullets or seat them long and reseat before the match/session.

Neck Wall Uniformity and location - you can measure this, and it is a variable you can control via neck turning and mandrels. How much variation is too much depends on accuracy expectations, and there probably isn’t any hard data on variation and it’s correlation to bullet release variation. We can all agree that a consistent radius on the interior of the neck is more beneficial than a consistent exterior radius (mandrels to push inconsistencies outward).

Elasticity - Also controllable via a suitable and equally importantly... repeatable method. No, your BIC lighter, nor your drill and a socket would be considered repeatable. For the crowd that anneals every “X” firings... Is iteration 2, 3 & 4 the same as freshly annealed necks if you anneal every 5 firings?

“Grabbiness”- Many things effect this variable. Dry tumbling vs wet tumbling vs no cleaning have an effect. Bullet coating has an effect. Neck tension, thickness and elasticity have an effect. Annealed vs not annealed for that particular iteration has an effect beyond elasticity. In my opinion, with everything else being ideal, this is the biggest wavering variable from one loading session to the next. Control this to the best of your ability by doing case prep the EXACT same every time. Brushing necks will help, as will a dry neck lube. Annealing every time will also help vs annealing every X firings.

Main point is this; that you may not have a grasp on everything that influences the total effect of your neck tension, but the more consistently you prep your cases, the better off you will be in consist neck tension and bullet release.
 
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#45
SicVic said:
So I have my opinion and I load accordingly.
I talking about a bolt gun ( mine is 6.5 CM)
Please don't write a novel or attach a bunch of tutorial links; just a few quick highlights will do.
If you think it does 3 jobs then put them in order.
I would like to see what the prevailing thoughts are.
Again, I'm not asking to be taught just asking what you think it does.
Click to expand...
Here is general answer:
  1. If tension is too low, then you will get bullet setback badly because when loading bullet into chamber the bullet will push far down into the case (if its not compressed). This will be common in AR15's if you do too little tension because of the angle the bullet goes from magazine to chamber, length of bullet matters in this...obviously.
  2. If tension is too low, and its the other way, or compressed load, your OAL will grow, or the bullet will just fall out (If powder is up in the neck and its that compressed)
  3. IF tension too low and bullet OAL grows, it might put bullet into lands, and cause pressure spike.
  4. If tension too tight, more than say.... .04, which is more than normal, because normal would be .002 or .003, and benchrest might be .001, your accuracy will suffer slightly because ES will vary more.
  5. If tension is too light, and seal not tight, it might not be sealed great and moisture could possibly get in, rare but possible, and that would be very light tension under .001 I would guess.
generally speaking, seat to .002-.003 neck tension for normal shooting applications.

This is strictly about neck tension, I did not mention crimping, which is a totally different topic.

I hope this helps. Sorry about the mean people. They didnt get enough bullying skinny geeks in high school, so they troll forums waiting for people to post basic questions, that they think everyone knows.
 
#46
Being a Marine I can handle being kicked around a little bit...as long as its not from the Navy Dudes.

Very detailed explanation and informative references!
Towards the end of your posting you referenced tension amounts (.004", .002", .001") and associated the .001" tension with a Benchrest shooter.

Do you think that lighter tension inherently produces more accurate ammunition? Just asking your opinion or thoughts on this.
Don't go overboard as I know this subject can get really drawn out.

Vic
 
#48
SicVic said:
Being a Marine I can handle being kicked around a little bit...as long as its not from the Navy Dudes.

Very detailed explanation and informative references!
Towards the end of your posting you referenced tension amounts (.004", .002", .001") and associated the .001" tension with a Benchrest shooter.

Do you think that lighter tension inherently produces more accurate ammunition? Just asking your opinion or thoughts on this.
Don't go overboard as I know this subject can get really drawn out.

Vic
Click to expand...
If benchrest does it, that means if you are benchrest, you should do it. This has been heavily studied. non benchrest, its not good. as I said
 
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#49
SicVic said:
You guys are good.
So I've posted this because I'm fishing for the general mindset of what tension does as I'm in the process of making another video on the subject.

Here's a scenario: Two test groups, same charge, same brass, same development. Everything is the "same" as you can get it.
One group seated at .003" tension or 45# press weight one has zero tension set into the case mouth by hand.
Now what happens since neck tension is the all deciding factor??
Click to expand...

If you can push them in by hand, they're probably not going to stay put during recoil in the magazine.

If you live in a high humidity area you'd better have something between the cu and brass or you'll have varying degrees of force required because of the corrosion.
 
#50
Unfortunately, testing neck tension .003 vs zero tension wont work, because the zero tension will be ES all over the place. As it cant keep OAL, and is variable. So what I think you meant is basically .001 vs .003. There are too many variables in handloads to determine outcome of such a test unless you do it through say 10,000 rounds maybe. or very high number in climate controlled conditions.
I have already tested it, many times, and did not a page about it because results in small lots are completely inconclusive.
www.natoreloading.com
I load extremely precisely, with some of the best equip money can buy. Virtually no run out, neck turned, and measure internal capacity of the brass for tests. Basically, .001 neck tension is about ~30-40 PSI of seating pressing in a 223.
5e73f4fd-d152-453b-9e25-1101c76d33ae

Those are a few of my presses with chamber die. Runout is less than 1k, and I shot dozens of groups with 30-40PSI neck tension, neck turned brass vs 60 PSI, 80 PSI, etc. There is no conclusive "Oh, I see now" moment, and the national match guys got same result. Guys tinker with this, thinking, "oh, the round with the variable neck tension is going to be the flyer". Its not the case. There is too many variables involved to say neck tension alone makes accuracy. You wont know whether its neck tension, or the bullet wasn't consistent BC, or 10 other factors. Its too complex. The best you can do is make everything as consistent as possible, and then practice your shooting skill.
 
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