CBTO and neck tension

[Tucker65]

If your seating die stem doesn't fit the profile of your bullet very well I can see how you could very easily be off this much.
I haven't personally done this but I've heard where guys have used epoxy or bedding compound and bedded the bullet to the seating stem. This would give the stem full contact with the bullet so that any ram movement would make the bullet go into the case instead of some of the force trying to seat the bullet into the stem.

John

 

[Straightshooter1]

How does ogive difference correlate to meplat?

Hmmm??? In terms of BOAL vs BTO?

 

[mikecr]

How does ogive difference correlate to meplat?

It doesn't. The meplat can be anywhere regardless of ogive radius.

Also, there is not a direct correlation to ogive radius variance and CBTO.
There is a change of nose datums, which directly affects a BTO measure, but BTO is not CBTO.

An example for CBTO could be with seating a bullet having lower cals of ogive radius.
The stem would not ride up the nose as far, so it would seat the bullet in deeper. But, the CBTO tool also would not ride up the nose as far, so it would tend to make the bullet appear seated less, -except the bullet was seated deeper. So CBTO remains pretty much as you had set it.
Just opposite with a bullet that has greater cals of ogive radius, still stable in CBTO, due to this effective counter measuring.
Now add inconsistent seating forces, and you're back to variances in CBTO anyway...

If with this variance, the CBTO remains stable, bearing/base seating depths are varying, but rarely enough to matter. CBTO is far more important than normal variances in bearing depths.
Look at your calipers and set 5thou of what could be bearing seating variance. 5thou of neck length.
How much do you really think that matters to case capacity, or to neck tension?
Given all the other variables, I'm sure you could not prove to yourself that it matters.

 

[INTJ]

I apologize but I don't quite understand why this should matter. The die is set up in certain way and the stem touches the bullet the same way every time. My question refers to consistency in seating bullets. In other word, I am interested in improving my process and excluding variations in seating depth.

It's because the seater stem doesn't contact the bullet at the ogive. It contacts the bullet much closer to the tip. If you measure the bullets at the seater contact point you will see as much variance as there is at the ogive. So even bullets with the same ogive measurement can seat differently if the seater contact point isn't the same as well.

 

[mikecr]

The biggest bang for the buck is to manage seating friction, because if you want consistent seating then the seating forces need to be consistent.
A bunch of annealing, and cleaning, is really counterproductive to this.

 

[marchx]

Yes, indeed.
If you take 3Bs:barrel, bullet, brass, I don't understand well enough the sophistication of brass prep. If you take a piece of brass, you clean it, anneal it, trimm it, size it you still can get different neck tension. I feel unable to properly trace my errors. I am wondering if I should skip the mandrel after neck sizing with a bushing.

Btw, other people were asking about the bullets- it's berger's bt target.

 

[RegionRat]

Yes, indeed.
If you take 3Bs:barrel, bullet, brass, I don't understand well enough the sophistication of brass prep. If you take a piece of brass, you clean it, anneal it, trimm it, size it you still can get different neck tension. I feel unable to properly trace my errors. I am wondering if I should skip the mandrel after neck sizing with a bushing.

Btw, other people were asking about the bullets- it's berger's bt target.

There is much in common between most games that chase accuracy for score, varmint shooting, etc.

Many of the tools and methods overlap between F-Class and BR for example. However, once you get close to the state of the art, there will be some debates in public forums about the best path to a goal.

What is your goal? Are you focused on seating depth to state of the art, or shoulder datum length to state of the art, or seating force to state of the art, etc.?

Back at the front of the string you asked about seating depths but your opening also stated you don't keep your brass organized by firing cycle.

Whatever comes from all the posts, my advice is the following. Take a batch of high quality virgin brass and keep it separated from all of your mixed cycle brass. Using your best process after digesting all the input advice, prep some of your current mixed batch and the segregated brass. The purpose being to determine the effects of unsegregated brass effects from segregated brass effects. Both batches will have some natural dispersion in things like work hardening, friction, neck tension, seating depth, etc., but I have yet to hear anyone speak to keeping your brass batches more organized and not mixed.

Brass does fatigue regardless of annealing. The majority of the case does not get affected by annealing, but it is hard to predict the role that has in performance on the target. Even the debate on annealing or not is worth a look at keeping the batch on the same firing cycle versus a batch with mixed history just to determine the contribution to your goals. Again, just a suggestion to clear up your goals and to try a segregation based on firing cycles.

 

[Skeptic123]

I might have missed it but what kind of press are you using to seat your bullets? If you are not using an arbor press it is much more difficult to get the kind of consistency you are looking for. Also generally I find the same kind of BTO consistency in Berger boat tail match bullets. However the overall lengths of each will vary considerably. That creates different profiles in the ogive and depending on the shape of the bullet seater and the shape of your comparator, you can get measurement differences. I suggest you try sorting a batch of bullets by length and see what you get.

 

[Webster]

I must confess not to segregate 6BR brass in separate containers according to the number of firings. My bad.

So, after cleaning my brass I anneal it (2.7s in my induction annealer. Tempilaq changes its colour at 2.6s). However in one batch of brass I can have 2 cases fired 3 times, 1 case fired one time and 30 cases fires 4 times. Even though I anneal the brass I think that still the brass fired one time has a different level of hardness than a piece of brass fired 4 times and annealed after every firing.
When I seat a bullet in a case fired one time the CTBO is 0.003 shorter in comparison to seating a bullet in a 4-times fired case (annealed).

In order to achieve the same CBTO I seat the bullets long and see where I am at. Then I adjust the final seating depth.
I understand that the difference in neck tension is still there. What should I do?

I always wondered if repeated annealing would cause the neck hardness to return to the same hardness. On the AMPS website they repeated annealing on the same case and reported you always got about the same hardness. It doesn't seem reasonable to me but that's what they report.

 

[Ned Ludd]

How are you supposed to address this issue?

One method is the use of a tool such as Bob Green's Comparator:

Welcome to Green's Rifles

Complete Bench & Varmint Rifles Precision Barrel Installation Superior Custom Dies and Tooling Specializing in craftsmanship

greensrifles.com

This tool and those like it basically measure the bullet nose length variance between the seating die stem contact point where the die pushes the bullet down into the neck, and the caliper insert contact point where we measure CBTO. In other words, you are sorting sort bullets into groups where the distance between the two contact points are more uniform, thereby improving seating depth consistency.

Another method that I refer to as sort of a "poor man's" Bob Green tool is to simply sort bullets by OAL into length groups. In my hands, the majority of bullet OAL variance resides in the nose region, rather than the bearing surface or boattail segments. That may vary by brand, but I shoot mostly Berger bullets, with a few Sierra or Hornady bullets, and they behave the same way in my measurements. Because the majority of bullet OAL variance resides in the nose region, sorting bullets by OAL will allow one to minimize length variance between the two critical contact points, both of which reside in the nose region. It's just a simpler/easier way to approach the issue that doesn't require the purchase of an expensive tool, with the caveat that the results may not be quite as rigorous as when using the tool. Nonetheless, length-sorting bullets by OAL can help improve seating depth (CBTO) consistency.

 

[marchx]

Amp's manufacturer does not disclose all facts. In particular it does not reveal how aztec determines proper annealing time. How do we know that the time chosen by aztec is the most appropriate from the recrystallisation perspective?Amp is just a black box accompanied by several declarations of its manufacturer.

 

[Jennb]

Thoughts to help keep it simple!

There will always be variance in seating pressure even with identical brass. Annealing keeps the brass from getting hard and splitting. Different number of firings on the brass will add to the equation because of work hardening even with annealling
Since is your brass is all mixed together you will have to be diligent about watching necks for cracks.
Sort your loaded ammo by seating pressure if you have a big difference and shoot it in order, heaviest to lightest or the other way around. Now use an ogive tool to check your seating depth and make them all the same or sort your bullets BTO and load them in those groups. 2 thousandths seating depth on the ogive can make a difference on target because it is where your bullet touches the rifling first.

 

[JFrank]

@marchx
Recommend you buy a fresh box of brass, keep them on the same cycle and loose the annealing for the new batch.
If you do go back to annealing, use a 10 piece sample to compare against the other over time.

 

[BoydAllen]

A friend whose degree is in metallurgical engineering told me that the result of annealing relates to the degree of work hardening. Specifically, if you do the same annealing procedure to brass that has been work hardened different amounts, that the results will vary accordingly. I do not think that most shooters know this. Also, for cases we are not doing full annealing to a dead soft condition. One way that I have found useful to gauge degree of partial annealing is to look at shoulder bump uniformity. If you start with a time that does not accomplish this, and increase time in small increments you will come to a point where shoulder bump becomes a lot more uniform, and necks retain some spring.

 

[mikecr]

All that's needed is correct temperature range and sufficient time for grain recovery. Additional time makes no difference -if the temperature is correct to begin with.

So that does not apply with a torch, or with induction, because the temperature is not a set/stable correct value. It does apply with dip annealing, where your medium is a set lower value (like 800deg). Here, you could dip necks all day, and grain growth will just reach a certain amount(within a couple seconds) and go no further beyond -at that temperature. Raise the temperature from there, and grain growth will continue over time, possibly all the way to FULL anneal (ruined) if raised enough.

I view torch or inductive as functionally the same. Both would take trial & error to hit on good results.
As long as folks manage that, and are happy with it, they're good.
I would not be going by glow color, temper, or tempilaq though. If not for dip annealing, I would probably go the AMP route.

 

[BoydAllen]

All that's needed is correct temperature range and sufficient time for grain recovery. Additional time makes no difference -if the temperature is correct to begin with.

So that does not apply with a torch, or with induction, because the temperature is not a set/stable correct value. It does apply with dip annealing, where your medium is a set lower value (like 800deg). Here, you could dip necks all day, and grain growth will just reach a certain amount(within a couple seconds) and go no further beyond -at that temperature. Raise the temperature from there, and grain growth will continue over time, possibly all the way to FULL anneal (ruined) if raised enough.

I view torch or inductive as functionally the same. Both would take trial & error to hit on good results.
As long as folks manage that, and are happy with it, they're good.
I would not be going by glow color, temper, or tempilaq though. If not for dip annealing, I would probably go the AMP route.

This experiment demonstrated that what you said is not correct. It shows a difference in grain structure with different times holding at 800 degrees. https://vacaero.com/information-res...rmation-and-annealing-of-cartridge-brass.html

 

[mikecr]

I suppose I'm stubborn but what I'm missing in their experiment was how they annealed.
How did they heat what thickness of metal, measure that temperature, and when did they start their timing?
If they just placed the samples in an oven, it would take a while for the metal to reach the oven temperature through it's thickness. This is a company that sells furnaces.
With dipping, both the inside and outside surfaces are exposed, and I believe that a bath of 800degF provides a good process anneal for formed cartridges, within seconds. The time it takes to dip and pull out.

I may be wrong. I have no way to measure with certainties.
But I am sure that I do not need to dip my brass in an 800deg bath for 30minutes, and I know that I do not want my brass too soft. I just want it relaxed enough for body/shoulder forming, and normalizing of neck tension.

 

[Ned Ludd]

This experiment demonstrated that what you said is not correct. It shows a difference in grain structure with different times holding at 800 degrees. https://vacaero.com/information-res...rmation-and-annealing-of-cartridge-brass.html

In fact, annealing brass is a function of both time and temperature. There are numerous rigorous scientific papers demonstrating this if you care to scour the internet. The reason for selecting the temperature range most reloaders use is time-based. They want their brass sufficiently annealed, without taking several minutes, or even longer, for each case, although that could be certainly be done at slightly lower temperatures if they were willing to take a lot longer to do it. Most reloaders are not annealing their cases to the point where they are approaching becoming too soft. Instead, they anneal them to the bare minimum amount that accomplishes their goal with regard to seating force; i.e. they are targeting the lower end of the annealing window, not the upper.

Although there may be minute differences in annealed brass depending the initial amount of work hardening done to each piece before the annealing process, the real question is whether those differences are so minute that no one can ever realistically shoot the difference. The difference in work hardening among pieces of brass all fired in the same rifle with the same load are not work talking about. Further, it is worth note that because many reloaders are only annealing their brass very close to the minimum time and temperature necessary to get the desired effect, especially when using induction-type annealers, that over an increasing number of firings, the annealed brass ends up farther and farther from the original annealing status that was achieved the first time it was fired and annealed. In other words, the relative hardness of the brass increases over time because it no longer being fully brought back to the ground state after each firing/annealing cycle. If such brass is fired/annealed enough times using an annealing process that was barely sufficient to fully anneal it after the first firing, it will no longer be fully annealed after as few as 4-5 firings. I view this as a much greater concern than any possible minute differences in the amount of work-hardening each piece of brass receives and how that may affect the next annealing step, because the shooter can tightly regulate the treatment of their match brass, such that each piece they use in competition has always seen the exact same treatment (work hardening) as all the others.

 

[BoydAllen]

None of us is fully annealing brass. That would make it too soft to be useful. You can tell if you are getting what you were before, if that was just barely enough to uniform shoulder bump. If subsequent annealings at the same temperature and for the same amount of time are not getting you there (uniform bump), you can see that by looking at shoulder bump uniformity, and adjusting time as needed. In the post that I referred to you said that the advantage of immersion annealing at 800 degrees is that the grain size would not vary with additional time. Your most recent post contradicts that. ???

 

[Jennb]

If you can afford it the AMP annealer is the way go!