Neck Tension Effect on Accuracy

[bigedp51]

Below is from German A. Salazar's "The Riflemans Journal" in reply to a question about partial full length resizing which he did not
recommend.

Below he is talking about the benefits of "full length resizing in relation to the cases fit and alignment in the chamber.

Mr. Salazar often quoted the late Jim Hull of the Sierra ballistic test lab who also favored full length resizing.

Below is Jim Hull's humorous quote about full length resizing.

"The case should fit the chamber like a rat turd in a violin case."

Below Mr. Salazar is describing the full length resized case and its fit and alignment in the chamber.

Reloading: Partial Neck Sizing
by German A. Salazar
http://riflemansjournal.blogspot.com/2010/06/reloading-partial-neck-sizing.html

"Now the last scenario, a full-length sized case in which the neck is also fully sized. There is clearance at the neck and in the body of the case, the closest fit anywhere is the bullet in the throat. If the neck to bullet concentricity is good (although it needn't be perfect), then the bullet will find good alignment in the throat and the case body and neck will have minimal influence. Let's not forget that the base of the case is supported by the bolt face or the extractor to a certain degree as well; this is yet another influence on alignment. As you can see, there are several points from base to bullet that can have an effect. My procedure is to minimize the influence of those that I can control, namely the case body and neck, and let the alignment be dictated by the fit of the bullet in the throat and to some extent by the bolt's support of the base. Barring a seriously out of square case head, I don't think the bolt can have a negative effect on alignment, only a slightly positive effect from minimizing "case droop" in the chamber. Given that a resized case will usually have a maximum of 0.001" diametrical clearance at the web, this isn't much of a factor anyway."

If you do a search here and look up "Kevin Thomas" who worked under Jim Hull and later ran the Sierra test lab and who now shoots for Team Lapua USA you will find more full length resizing advice. (The rat turd in a violin case)

 

[Mikecr]

The subject here is neck tension..

 

[bigedp51]

The subject here is neck tension..

The subject is why the OP groups opened up when he changed from Redding full length die to a Forster bushing bump neck sizing die.

Meaning the OP groups became larger when he only necked sized his cases. And my point is even the Whidden die website tells you they get more concentric ammunition with non-bushing full length dies. And whidden also sells expander ball sets to control neck tension.

And what I'm saying is it may not be a neck tension problem but the type die he is using. The OP best groups were with a full length Redding die and Forster does not make full length bushing dies and only makes neck sizing bushing dies.

I have been working with my Winchester 70 Ext Weather in 7mm RM over the past several months and have been perplexed with changes in group size. After carefully breaking-in the barrel, I found a very accurate load of 68.6 H1000 in Nosler cases with a Hornady 162 ELD-X bullet and F215 primer. My 3 shot groups were 9/16 to 3/4 inch.

During later range sessions I found that groups had opened up to 1 1/2 to 2 inches.
Looking back trying to analyze what changed, I realized that I had switched to Forster bushing dies, and that I was carefully setting the neck tension at .002. Comparing that tension to my initial Redding FL dies, I saw that my polished expander ball was giving me .004 tension. So, would that increase in the initial neck tension produce better burning of the powder and better accuracy? Nothing else has changed - charges, cases, bullets all weighed and segregated and necks turned on the cases.

I can't get to the range for several days, but I'm intending on loading several rounds with tighter neck tension than .002. Any thoughts on this dilemma???

 

[billigoat]

Tagged

 

[Mikecr]

The subject is why the OP groups opened up when he changed from Redding full length die to a Forster bushing bump neck sizing die.

No, read the subject and OP's questioning again -> "Neck Tension Effect on Accuracy".
Your own 1st reply was purely about tension.

But I follow what you're suggesting about the sizing change as a factor.
He should have expected result change with this,, could have been better or worse until load developing with such a condition.

 

[bigedp51]

No, read the subject and OP's questioning again -> "Neck Tension Effect on Accuracy".
Your own 1st reply was purely about tension.

But I follow what you're suggesting about the sizing change as a factor.
He should have expected result change with this,, could have been better or worse until load developing with such a condition.

Well forgive me for reading the OP first post again and re-reading all the other posting going off in the wrong direction.

The OP was getting the best accuracy when his "full length resized" cases fit the chamber like a rat turd in a violin case.

And his groups opened up when he neck sized the cases using a bushing die.

The reason I say this is because I have a Forster bushing bump neck sizing die and it produces more neck runout than any other die I own.

Advanced Reloading — Checking the Geometry of Neck Bushings « Daily Bulletin

Not only can the bushing itself induce neck runout, if the neck diameter of the case is reduced .005 or more it also can induce neck runout. This is why it is recommended to size the neck in two steps when reducing the case neck .005 or more.

"IF" the OP checks his neck and bullet runout with both sizing methods and posts the results we might get to the bottom of his problem.

 

[Stoneke]

Well, I did run a check on several loaded cases that had used each method of resizing. Out of six cases with the full length die, the run-out ran from .0007 to .002. With the bushing die, run-was was .0005 to over .004. I used a Hornady Concentricity gauge, which allows reading an estimated figure to the ten thousandth place and provides for a correction arm to reduce the final run-out. So, it seems as though the bushing die comes in at second place. All cases were same mfg and neck turned.

 

[Mikecr]

Your runout is far higher than you think.
You might figure out the cause of your runout beginning with v-block type runout gage (not a neck bender). Then knowing the cause, you can fix it.

 

[bigedp51]

Well, I did run a check on several loaded cases that had used each method of resizing. Out of six cases with the full length die, the run-out ran from .0007 to .002. With the bushing die, run-was was .0005 to over .004. I used a Hornady Concentricity gauge, which allows reading an estimated figure to the ten thousandth place and provides for a correction arm to reduce the final run-out. So, it seems as though the bushing die comes in at second place. All cases were same mfg and neck turned.

The Hornady gauge will read approximately half of what the Sinclair concentricity gauge does. Meaning your figures would be .0035 to .008 and .001 to .008.

The advantage of the Hornady concentricity gauge is it holds the full length resized case just like it would be in the chamber. Meaning supported by the bolt in the rear and by the bullet in the throat. And not rotating on the body of the case like the Sinclair gauge and measuring with a out of round case body.

 

[Mikecr]

The advantage of the Hornady concentricity gauge

There is no 'advantage' to it, nor to 'rat turds in a violin case'.

Consider indicating the arc of a jump rope in action. You could place the gage nearest one pinned handle of the rope(line#2 pic) -> if you purposely want very low % of arc indicated. This is the lie behind neck benders.
Now consider the rope frozen rigid in it's arc. Pin and spin the rope from it's center while indicating nearest one of it's free handles(line#6 pic). Here you read the full amplitude of it's arc. In this condition you'll know the rope is truly straight when it is(line#5 pic), and not until then.

Ammo is straight when verified so on a v-block gage. With this, it chambers without case tension(chambered tensions), and excess clearances are no longer needed (as never desired) to relieve such a condition. It's a different approach I suppose. But I'm declaring that you CAN make straight ammo, and that's the best you can do.

When you deny these things and chamber bananas your whole life, you create chambered tensions similar to resting a thumb on your action during firing. Move the pressure point from shot to shot and grouping opens. For the folks who apparently gave up on making straight ammo(because they heavily FL size), sloppy clearances seem to alleviate the problem. Their guns shoot better with this. And sloppy clearances leads to more sizing, which leads to more runout, which needs sloppy clearances. Classic loop...

Opposite of this is understanding of, making of, and use of straight ammo.
With this, clearances can be tight, leading to less sizing, leading to less runout, needing less clearance. A different loop, and there are actual 'advantages' in this.
Different thread.

 

[bigedp51]

If the cartridge case does not have equal case wall thickness the thin side expands more when fired. And if you are spinning a egg shaped case with the body of the case in V-blocks the neck of the case and the bullet will show more runout than the bullet has.

On top of my statement above at German Salazars old website "The Riflemans Journal" the subject of warped brass and the base of the case not being square was covered in detail.

And since I read about the rat turd in the violin case at Mr. Salazars website first and repeated Kevin Thomas of team Lapua USA I will take their advice over yours. And Kiven Thomas worked in the Sierra ballistic test laboratory where all the ammunition was full length resized.
(Full length resizing = "The rat turd in the violin case")

I also find it amazing that someone developed a gauge to check for the very thing I posted about in my two postings.

Neco Concentricity Gauge
NECO Product Descriptions

Also referred to as "The Case Gauge," this item is designed to measure:​

1) The curved "banana" shape of the cartridge case;
2) The relative wall thickness variation of a cartridge case;
3) The cartridge case head out-of-squareness;
4) Individual Bullets - out-of-round "egg shape" and/or
curved "banana" shape (excepting very small bullets);
5) The seated bullet and cartridge runout of loaded rounds. The accuracy of any firearm is determined -- and limited -- by the quality of the ammunition shot in it. The effect of imperfections in ammunition is cumulative; each flaw adds to the influence of all others. Precision shooters spend much time and effort "uniforming" cartridge cases, using advanced techniques to eliminate variation. Yet until recently, one of the most important of these variations has not been susceptible to detection by any device readily available to marksmen.


And at Accurateshooter.com they say the same thing...
The case body "must" be in alignment with its axis,

Bullet Concentricity Basics — What You Need to Know

Bullet Concentricity Basics — What You Need to Know « Daily Bulletin

 

[cape cove]

So, guys, what would you think to be the best kind of gage to measure runout, the Hornady type or the RCBS v- block type.

 

[243winxb]

Well, I did run a check on several loaded cases that had used each method of resizing. Out of six cases with the full length die, the run-out ran from .0007 to .002. With the bushing die, run-was was .0005 to over .004. I used a Hornady Concentricity gauge, which allows reading an estimated figure to the ten thousandth place and provides for a correction arm to reduce the final run-out. So, it seems as though the bushing die comes in at second place. All cases were same mfg and neck turned.

Compare on target. 2 , 5 shot groups of each. May not see a lot of difference till past 300 yds.

 

[bigedp51]

So, guys, what would you think to be the best kind of gage to measure runout, the Hornady type or the RCBS v- block type.

I have both type gauges so I can argue with people like Mikecr.

The Hornady gauge holds the case just like a chambered full length resized case in the chamber.

It is supported by the bolt face in the rear and the bullet in the throat. And the body and neck of the case never touch the chamber walls. Because the full length die reduces the body diameter .003 to .005 in the average die.

Meaning even if the case body is slightly out of round the body of the case has no guiding effect on bullet alignment. (rat turd in a violin case)