Neck Tension Basics

J

JimBarshinger

Guest
Hi, I was wondering if you guys could give me the basics on neck tension. I have read in a few places that some powders need more neck tension than others, N133 being one that is mentioned as needing a lot of neck tension. Is there a good all around neck tension to start with? As a starting shooter, should I just pick one and not bother with trying to fine tune for now? Anyway, was hoping you guys can give me some pointers.

Thanks,
Jim
 
I neglected to mention, I am shooting a 6mm PPC with 0.262" neck.

Thanks,
Jim
 
Neck tension measurements?

JimBarshinger said:
Hi, I was wondering if you guys could give me the basics on neck tension. I have read in a few places that some powders need more neck tension than others, N133 being one that is mentioned as needing a lot of neck tension. Is there a good all around neck tension to start with? As a starting shooter, should I just pick one and not bother with trying to fine tune for now? Anyway, was hoping you guys can give me some pointers.

Thanks,
Jim
Click to expand...

Good question. I don't have an answer, but I hope you don't mind me asking a related question here: Does anyone measure neck tension during the loading process, as in measuring the force required to seat the bullet? I have observed (qualitatively, just by feel) that after several loadings, some cases can take noticeably more or less force to seat the bullet, and it stands to reason that these rounds may produce fliers. Some very limited testing (just two rounds so far) confirmed this. So once you find the magic level of neck tension that gives best accuracy, how do you ensure that every round all season long has that same neck tension? Some are measuring powder charges down to 0.1 grain. How do you keep neck tension variation down to say 1 oz?

Thanks,
Keith
 
Jim

You should ask the one person who can give you the real answer. That is, Mr. Rifle. Start with a nominal tension, say .002" or .003", work up to your best load, then vary the tension in increments, in both directions. Mr Rifle will tell you if one is better than another. You'll need a supply of bushings to do this. Make sure that they are all of one brand.

Good Luck

Ray
 
Jim ...

I shoot a Billy Stevens built 6PPC with a .262 neck and use Bart Sauter's Bullets. Both Billy and Bart recommended a .257 bushing with V133 and it has worked out great. I turn my necks so that with a bullet seated the OD measures .2605". ;)

For more on neck tension take a look at this: http://www.benchrest.com/FAQ/2.4.shtml.
 
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Yes. The other piece of information that you need is loaded round neck diameter, over the bullet's pressure ring. Neck tension, as I use the term, is the difference between the diameter of a sized case neck, and the diameter of the neck, over the pressure ring of a loaded round. I turn my necks to .0087, and use a .257 bushing. I went to this bushing size because it was suggested to me by Del Bishop, and I noticed an improvement in accuracy, with 133. One thing that you should know about this setup is that the more neck tension you use, the more critical seating die to case fit becomes, particularly with flat base bullets. I switched to a Nielson seater because its much closer fit gives me straighter ammo.
 
When I asked for neck tension, I guess what I really was asking for was the amount of reduction in neck dia beyond the size of the bullet for different powders. For instance if the bullet is .243 then 0.002" of reduction would be .241. The actual tension of course depends on the wall thickness and elasticity of the case neck. I have a .258" bushing for my neck sizing die and I also have a Redding small base die that without the expander ball, gives less neck sizing than the .258" die. I am guessing that the neck of that die is .259 or .260. I read somewhere that N133 required .003 or .004 of neck tension while H322required less, like .002. So, I just wanted to get an idea of what people were using. I would like to use the Redding small base die without the expander because the resized brass with this die has less than 0.0005" or runout - a bit less than the neck die with bushing, but wasn't sure if I would be getting enough neck tension.

Thanks,
Jim
 
Pressure Ring + Brass Thickness - Bushing - Springback = Nominal Tension

Right?


I have a .332 neck. I'm wanting at least .001 clearance. My bullets are .3083, but I'm allowing for .3087.

So, ( .332 - (.001 * 2) - .3087 ) / 2 = 10.65 Thousandths.

My .332 is actually a skosh less than that, so I trimmed to 10.5.

Does that sound reasonable?

Now, my current bullets are .3083.

.3083 + .0105 * 2 = .3293

I'm currently trying a .327 bushing. The N120 that I'm using, from what I've been told, doesn't like a lot of tension.

Does that all sound reasonable?

Greg J.
 
SGJennings said:
Pressure Ring + Brass Thickness - Bushing - Springback = Nominal Tension

Right?


I have a .332 neck. I'm wanting at least .001 clearance. My bullets are .3083, but I'm allowing for .3087.

So, ( .332 - (.001 * 2) - .3087 ) / 2 = 10.65 Thousandths.

My .332 is actually a skosh less than that, so I trimmed to 10.5.

Does that sound reasonable?

Now, my current bullets are .3083.

.3083 + .0105 * 2 = .3293

I'm currently trying a .327 bushing. The N120 that I'm using, from what I've been told, doesn't like a lot of tension.

Does that all sound reasonable?

Greg J.
Click to expand...

Well, define reasonable! :D:D

I just measure the neck of a loaded round,

And measure the neck of a fired round,

And measure the neck of a sized case,

And write down the measurements,

And look at the 3 numbers,

And adjust accordingly.


Seems to me that this eliminates measurement tolerance stack, math errors and checks the final product FOR REAL...... as it sets, ready for the chamber.

Me and math don't get along well.

BTW...... If you DO do all the math and yet DO make a mistake and you DO get your necks too thick :)eek:) and you DO try chamber the "unsafe round" (!!:eek::eek::eek::eek:!! then one of two things will happen...

The round will chamber,

Or it won't.

If it won't, obviously don't force it.... and if it WILL, it's safe. It might not SHOOT well, but it's safe.

I define "amount of neck tension" by comparing the difference between a sized neck and a slip-fit neck. If a bullet is a slip-fit, zero clearance in the neck and it measures .329 on the outside using a mic or caliper, and if I size it with a bushing that results in an outside diameter of .327 (without bullet) then I describe this as ".002 tension" or two thousandths interference fit.

:)

al
 
That sounds a lot like a 30BR. I keep hearing they're way too forgiving......That's why I'm building one now..........ok another one.
 
I measure my necks with a micrometer after I load as well. But, after making some mistakes, I now check every single case when I'm trimming with a neck thickness micrometer. That's be a PITA to do loading a bullet and checking.

It's a 30 Major. Necked up 6.5 Grendel.

Greg J.
 
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Greg

That .001 loaded round clearance seems a little tight for a 30. I think I am safe in saying that most 30 shooters go for .002. With my 30 BR, which has a .330 neck, I go with a loaded round dimension of .328. I use a .325 neck bushing.

With my .269 neck 6PPC. I shoot for a loaded round of .2675, erroring on the loose side. I use a die that measures .2655.........jackie
 
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JimBarshinger said:
Hi, I was wondering if you guys could give me the basics on neck tension. I have read in a few places that some powders need more neck tension than others, N133 being one that is mentioned as needing a lot of neck tension. Is there a good all around neck tension to start with? As a starting shooter, should I just pick one and not bother with trying to fine tune for now?
Click to expand...
I'm a little confused. Winning -- doing real well -- is all about fine tuning.

As you say, different powders do seem to like different neck tension. Here is one from column B -- different seating depths can, too. In effect, a jammed bullet is similar to using higher neck tension as far as the development of first bit of the pressure curve. If you jump bullets, you may find that a higher neck tension is beneficial. May not, too.

I know, jamming bullets -- sometimes quite a bit -- is Holy Writ.

Another thing to consider in this long journey called benchrest is what gives you the most consistent performance. "Dots" one time and "splots" the next is not conducive to winning, or even learning anything useful. If seating bullets .020 off -- or even .040 off -- with a heavy jam gives better overall performance in your rifle, you have a decision to make.

As Ray said, "Mr. Rifle" will express his preferences, if you let him.

Good luck to you,

Charles
 
Neck tension

mks said:
Good question. I don't have an answer, but I hope you don't mind me asking a related question here: Does anyone measure neck tension during the loading process, as in measuring the force required to seat the bullet? I have observed (qualitatively, just by feel) that after several loadings, some cases can take noticeably more or less force to seat the bullet, and it stands to reason that these rounds may produce fliers. Some very limited testing (just two rounds so far) confirmed this. So once you find the magic level of neck tension that gives best accuracy, how do you ensure that every round all season long has that same neck tension? Some are measuring powder charges down to 0.1 grain. How do you keep neck tension variation down to say 1 oz?

Thanks,
Keith
Click to expand...
G'Day Keith,i get over this by annealing my cases when this starts to happen,cases out of the same batch work harden differently i have found, it must have something to do with the composition of the brass, another way out of neck tension is to load with bullets stuck into the lands and seat when you close the bolt.Bruce
 
brutal said:
G'Day Keith,i get over this by annealing my cases when this starts to happen,cases out of the same batch work harden differently i have found, it must have something to do with the composition of the brass, another way out of neck tension is to load with bullets stuck into the lands and seat when you close the bolt.Bruce
Click to expand...

Bruce,
Thanks for the response. I am thinking about trying annealing, too. But I wonder, if the brass work hardens differently, might it also anneal differently, which would still leave neck tension variation? Apparently, some shooters are concerned with this, since I found K&M makes a seating force attachment for their arbor press (http://www.kmshooting.com/catalog/a...ith_force-measurement_and_dial-indicator.html) and RSI makes a seating force load cell (http://www.shootingsoftware.com/recoil.htm). I wonder if anyone has tried either of these and documented an accuracy improvement by sorting for bullet seating force.

Larry Medler posted some measurements of seating force and the variation was large, but his one test did not show decreased muzzle velocity ES with rounds selected for uniform seating force (http://home.comcast.net/~jesse99/tension.html). He explains that the results may have been clouded by a powder that did not perform well in his gun. He now has an RSI system (http://home.comcast.net/~jesse99/LoadForce250.html), but admits he still hasn't proven that seating force makes a difference.

I would be interested in seeing data, if anyone has any, that documents the effect of seating force on accuracy.

Cheers,
Keith
 
mks said:
Bruce,
Thanks for the response. I am thinking about trying annealing, too. But I wonder, if the brass work hardens differently, might it also anneal differently, which would still leave neck tension variation? Apparently, some shooters are concerned with this, since I found K&M makes a seating force attachment for their arbor press (http://www.kmshooting.com/catalog/a...ith_force-measurement_and_dial-indicator.html) and RSI makes a seating force load cell (http://www.shootingsoftware.com/recoil.htm). I wonder if anyone has tried either of these and documented an accuracy improvement by sorting for bullet seating force.

Larry Medler posted some measurements of seating force and the variation was large, but his one test did not show decreased muzzle velocity ES with rounds selected for uniform seating force (http://home.comcast.net/~jesse99/tension.html). He explains that the results may have been clouded by a powder that did not perform well in his gun. He now has an RSI system (http://home.comcast.net/~jesse99/LoadForce250.html), but admits he still hasn't proven that seating force makes a difference.

I would be interested in seeing data, if anyone has any, that documents the effect of seating force on accuracy.

Cheers,
Keith
Click to expand...

I've messed with seating force and "bullet pull" quite a bit. At one time I was convinced it was important, now I'm not.

I mod'd an arbor press to accept a small torque wrench and messed with seating force and bullet pull to the extent of using as much as .012 interference fit, very thick necks made from full length cases, and even gluing bullets into place.

My "data" consists of pages of scrawled notes in my range notebooks..... never been collated simply because I was convinced it was all a waste of time.

opinionsby



al
 
alinwa said:
I mod'd an arbor press to accept a small torque wrench and messed with seating force and bullet pull to the extent of using as much as .012 interference fit, very thick necks made from full length cases, and even gluing bullets into place.

opinionsby

al
Click to expand...

Al,
Thanks for the "Alecdotal" data.;) These EXTREMES should reveal a difference, if there is one. Did you compare accuracy of rounds with high seating force variation (say, a mix of thin and thick necks) with those with low seating force variation (all thin)? Or were the comparisons of high force (all thick) versus low force (all thin)?

Thanks,
Keith

Thanks,
Keith
 
mks said:
Al,
Thanks for the "Alecdotal" data.;) These EXTREMES should reveal a difference, if there is one. Did you compare accuracy of rounds with high seating force variation (say, a mix of thin and thick necks) with those with low seating force variation (all thin)? Or were the comparisons of high force (all thick) versus low force (all thin)?

Thanks,
Keith

Thanks,
Keith
Click to expand...

I'll see if I'm reading you right. I'm thinking you mean mixing thick and thin necks in the interest of changing up neck tension.....

I've mixed 'em and matched 'em. I don't believe that neck tension itself has any measurable or even visible effect until you're down "in the ones" using short stubby point-blank bullets. And even then if you've got a good 6PPC barrel it's meaningless. THIS IS JUST MY OPINION! I've never had a tunnel. And once I've got a barrel really shooting I DO work to equalize all my neck tension on short range stuff. But I generally test barrels and loads by just slip-fitting the bullets. And unfortunately, even with only about a dozen short range barrels I'm finding that some barrels just SHOOT, and that some guns are better than others. I know this sounds trite and I don't know how to quantify it but sometimes you just KNOW in the first 20rds....... (I'll not explore this concept further!)


I really spent a lot of time with neck tension while trying to get VLD's to shoot, trying to "change the pressure curve" .......


I tried EVERY combination I could muster trying to make several no-turn 6BR's and .243AI's shoot...... shooting everything over a chronograph and meticklishly comparating and graphulating and analyticalizing to beat the proverbial band.

They flang fliers. I mixed and matched and manipulated in an effort to find WHY the stupid fliers.... I'd try loose and tight and then mix them and keep track looking for patterns. Trying to force a trend.

what I found was that neck tension just didn't do SQUAT. I had better luck with wicked thick necks using high neck tension and deep jam but no real joy. I made cases by necking down longer cases trying to get REALLY high tension.....Neck clearance was getting down close to .001 per side and still no repeatable performance. The necks were pretty rough on these home-made thickies, always worried I'd jam something in there and get a pressure spike...... so I'd turn a batch of necks all perfect, anneal and fiddle until they all were even and....... blechhhh still fliers.

I aligned my cases, weighed and sorted and culled and Juenked and bent and tweaked for zero runout and even neck tension always being careful to keep my clearance safe..

My best groups were still with the thick clunky necks and funky tension. And my velocities were all same-same. No perceivable change from thin to thick.

In the mean time my buddy started working with a new Lilja...... This Lilja was a .274 nk no-turn .243AI and bud's NOT a meticulous reloader. (I kept telling him to clean his necks up for even pull, just a cleanup cut on the neckturner..... but he wouldn't lissen :rolleyes:) His cases were TERRIBLE...... raggedy and black and ugly. Judging by looks, he dipped his cases in feces periodically and hammered a washer over the neck to get them to hold a bullet (meantime I'm reaming my necks prior to turning, massaging them lovingly into shape with multi-hunner'dollar dies, spinning them out in Nev'r-Dull and waxing them to a shine.... )


But the Lilja would shoot, this cobbled together abortion in an overbore chambering was out shooting me!

A new Krieger came in, and another Shilen. Couple new 6BR chambers, a .271 and a .268 ......... so I started messing with them. Just dropped the crazyprep, whipped up some brass and started "breaking them in".... (yeahhh, I useta' buy in on that one too :rolleyes: ) In fact, for the .271nk 6BR I didn't even turn those first cases....... just checked to see if they'd clear and went at it. (I'm just breaking in you see.....) Just load the cases, check them for slip-fit in my chamber-gizzie and blow them out clean so's I could neck-turn them later.

And ........ my fireform groups were AWESOME..... I'm PUMPED for when I get some good brass!!! Wheee, she's gonna' SHOOT then eh!

So I made up some good brass...... all turned and shined and perty.

and got my fliers back.

????

And the wee liddle light started to come on in my wee liddle haid.....

With VLD's it's all about CLEARANCE!!!!! Give the back of the bullet a nice tight guiding bushing and PULL THE LEVER KRONK!

fliers GONE.

ALLofa'SUDDEN officially shooting 1/4 inch groups using VLD's..... Whoopeee!!!

So all my tension experiments kinda' got set aside......

Later, trying to learn to tune PPC's I diddled with tension again. I tried to tune with neck tension. All's I found was that as interference fit increased, rounds got crookeder.

NOW.... to answer your specific question ;)

Mixing thin necks and thick necks in the same chamber/group:

100-200yd stuff (.22 and 6BR 14twist, 6PPC, short 30's) using "soup can" shaped bullets I can't see an accuracy difference between .001 and .004 clearance. Many others find that accuracy falls off when clearance gets under .0015 especially in the 30's. I haven't found this to be true. Here's my theory..... short-range, low-BC bullets with short noses and long bearing surfaces will gener'ly "self-straighten" into the bore. I personally use less than .002 and I do make them all the same, BUT...... When I first get a new chambering and I'm setting up my neckturner I always get 3-6 cases that are all over the map before settling in where I want to be. I use these cases up by testing them to destruction finding my maximum achievable velocities. They group fine...... I've done this recently with 30X47 Lapua and 300WSM. I'm not advocating sloppy neck thickness, in fact I'm anal about making my match brass all the same but the effect is small.

IMO :)

600-1000yd stuff.... for me this is 6BR, 6X47L and 300WSM..... using long bullets. IMO accuracy gets erratic if anything more than .002 total clearance is used. In mixing thin and thick necks it's easy to see. Too much clearance equals fliers for me. I believe this to be a GUIDANCE issue not a tension thing. I believe that long bullets must be started straight. I believe in-bore yaw to be a very real problem with VLD's.

Regarding tuning with neck tension, using tension alone to effect group size/shape. Not thickness, but tension. I'm currently not doing it because I can't get it to repeat. I can't make sense of it. I'm also not competing in short range BR. I use my 6PPC for practice and for mapping conditions. It's my baseline for testing other chamberings. I find my Borden-built 6PPC's to just SHOOT. I find my velocity node and use a proven combination of about .002 interference and touching the lands and I'm done, gun shoots better than me. Same for my .308-.200 and 30X47L which I'm hoping to use for HBR. These guns just shoot dots. All I mess with is powder charge to stay in the node for temp.

The other huge change for me is weighing charges. I've just solved a TON of problems this way. Weighing charges has blown away all sorts of chaff.

Interestingly enough, weighing charges is what got me down into single digit ES, I now probably COULD see the minute changes that neck tension "may" produce! Maybe I'll try it again one of these days. NOT a top priority though.


Per "Alecdotal,"

MANalive....... just wish't I'DA thoughta that!!!!

I'm'a steal it A'ight?? At least borrow it???

:D


al
 
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