Is it just age, or perhaps something else?

[JPB4BAMA]

My suspicion is that this is simply a function of brass life, but interested to hear if someone has other experience or opinions. Have experienced head separation before and had a separate thread on that related to early separation on some Norma brass, but I have never seen this particular issue before.

Case separation just below the shoulder.
Lapua 223 Match, converted to 223AI.
23 firings with anneal between every firing.
Full Length Sized, 0.002 bump
Loads are rather mild at 23.8 gr Lovex S062 ( SW Precision), 88 ELDM, 2680 MV
Primer Pockets are still tight

 

[wbm]

anneal between every firing.

IMO: there ya have it.

 

[K22]

I've never had a separation and I've used a number of brands of cases, and I don't anneal.

However, I retire the cases after about 15 - 17 reloads, carefully inspect every time before and after sizing and control the shoulder set back. I look for suspect incipient failures and retire those I find with those issues.

Almost all the failures I've had were neck cracks. I had a few incipient fatigue signs in some shoulder areas, mainly 243's. Usually the case will begin to show signs of a potential fatigue failure before the failure occurs but not always.

 

[mgunderson]

Wow 23 times reloaded on a 223 case. They don't owe you anything.

 

[M-61]

I wish I knew or was a metallurgist. I’m not and I don’t.
So this is merely my thoughts:
23 reloads is a lot even with a 223. And annealed Each time! I’ve achieved more than that in my 222
This was not an attempt to see how many I could do but there was/ is no visible reason to not to.
They have never been annealed.
Now if I were a metallurgist I may know that 23 times annealed is well past an acceptable number or not.
And of course a 222 or 223 in a bolt gun is easy on the brass. I have some cartridges where 6 times is a big number but it’s usually the primer pocket saying goodbye

 

[3Sigma]

23 firings = about as good as it gets.

How many times were they trimmed?

Just a suspicion, but by annealing each time, the transition from annealed to hardened brass was where it stretched each time, eventually thinning the case walls. Similar to case head separation, just in a different location.

 

[JPB4BAMA]

I wish I knew or was a metallurgist. I’m not and I don’t.
So this is merely my thoughts:
23 reloads is a lot even with a 223. And annealed Each time! I’ve achieved more than that in my 222
This was not an attempt to see how many I could do but there was/ is no visible reason to not to.
They have never been annealed.
Now if I were a metallurgist I may know that 23 times annealed is well past an acceptable number or not.
And of course a 222 or 223 in a bolt gun is easy on the brass. I have some cartridges where 6 times is a big number but it’s usually the primer pocket saying goodbye

Actually I am a retired Metallurgist but no longer have access to a failure analysis laboratory, which my guess would show fatigue failure due to age and repeated sizing, even post anneal. As stated I really just suspect that this is a case of age and use beyond reasonable engineering life, but as you so aptly stated there were no visible signs and I saw no reason not to continue to use them either. Not that I am against retiring brass, but I really would not want to put it out to pasture prematurely, especially if it is performing well.
The post was sort of a shot in the dark wondering if there is something that I was not considering, especially because of the rather unique location of the failure.

Thanks for the comments.

 

[JPB4BAMA]

23 firings = about as good as it gets.

How many times were they trimmed?

Just a suspicion, but by annealing each time, the transition from annealed to hardened brass was where it stretched each time, eventually thinning the case walls. Similar to case head separation, just in a different location.

No that I really don't track since it's an Ackley. But I would say maybe 3 or 4, and even there its just a skim cut and about half of the lot don't even engage the cutter head. But that is a really good thought. So on that line, do you have any general guidelines as to what might be considered a limit on trimming?
Thanks

 

[Bill K]

23 reloads, even with annealing, that brass finally gave out from over working/stretching at the shoulder area. You got your monies worth out of it.

 

[JPB4BAMA]

IMO: there ya have it.

Sure, I get it, but do you mind elaborating on of your thesis? There are multitudes on both sides of the subject of annealing, each with their valid points, and this is not an long discussion I wish re-open. But If there is actually something that I have not considered I would love to hear it.
Thanks

 

[JSH]

I have some 6 and 7TCU from LC brass. I lost count on how many times the 7TCU was loaded, over your number a little. I annealed every other time and only neck sized every other time.

The 6TCU brass was around 15-20 times. It wouldn’t chamber in a new rig I built. Ran it through a SB die and made 222 out of it. As 222 it has about 5 loadings on it.

 

[dgeesaman]

How many thou, on diameter, does your sizing die squeeze in the brass at or just below the shoulder?

I have some dies that push the upper case body in several thou, only to be blown back out every firing. (This aspect if sizing is unrelated to shoulder bump setting.). My custom dies keep this down to a thou or two. I could see how heavy sizing plus being below the annealing zone could lead to fatigue failure.

 

[SShooterZ]

How common is it to have separation that high on the case? I have some 6MM Remington that is showing signs high up on the case like this. Although a little below the shoulder.

 

[JPB4BAMA]

How common is it to have separation that high on the case? I have some 6MM Remington that is showing signs high up on the case like this. Although a little below the shoulder.

Personally this is the first time I have seen this up this high. Like many have said common near the case base/web with incorrect bump/headspace. Hope others will shed some more light on the issue.

 

[6.5 forever]

Interesting in that the only case head speration I have seen was in 223, but it was in a gas gun.

 

[JPB4BAMA]

How many thou, on diameter, does your sizing die squeeze in the brass at or just below the shoulder?

I have some dies that push the upper case body in several thou, only to be blown back out every firing. (This aspect if sizing is unrelated to shoulder bump setting.). My custom dies keep this down to a thou or two. I could see how heavy sizing plus being below the annealing zone could lead to fatigue failure.

Oh how I wish I still had a Lab and microscope. The location is not exactly below the annealing interface, however it is very close and may in fact be in a transition zone which combined with your question about how much sizing leads to a whole new though process. I'm about to actually measure this on a good sampling of the other cases in this lot and see.

Stay Tuned

 

[SShooterZ]

Personally this is the first time I have seen this up this high. Like many have said common near the case base/web with incorrect bump/headspace. Hope others will shed some more light on the issue.

Same for me. I've seen it down in the web area but not as high as your pics or the current brass I'm referring to.

 

[JPB4BAMA]

Oh how I wish I still had a Lab and microscope. The location is not exactly below the annealing interface, however it is very close and may in fact be in a transition zone which combined with your question about how much sizing leads to a whole new though process. I'm about to actually measure this on a good sampling of the other cases in this lot and see.

Stay Tuned

OK, I'll admit that it in academic at this point given the actual brass life, but it is interesting to study.
Sizing results in 0.0045 inches, which translates to a 1.2% cold reduction by compression. At the same time the neck is reduced by 8.8%. Therefore I am wondering if in the area of failure there is insufficient residual strain energy to initiate recrystallization and the repetitive annealing process which as at or near minimum temperature at this location is actually resulting in a grain boundary embrittlement by either excess grain growth or Zn dissolution?

 

[rwj]

Full Length Sized, 0.002 bump

How did you determine that a .002” bump was required?

 

[dgeesaman]

OK, I'll admit that it in academic at this point given the actual brass life, but it is interesting to study.
Sizing results in 0.0045 inches, which translates to a 1.2% cold reduction by compression. At the same time the neck is reduced by 8.8%. Therefore I am wondering if in the area of failure there is insufficient residual strain energy to initiate recrystallization and the repetitive annealing process which as at or near minimum temperature at this location is actually resulting in a grain boundary embrittlement by either excess grain growth or Zn dissolution?

If it's fatigue, you might attempt a dye-pen test.

.0045 is about normal IME for a standard die and factory chamber. I know Tony Boyer's standard for PPC cases is .001" sizing on diameter over the upper body of the case. That's for single shot / match shooting, so in practice on repeaters i aim for .001 to .002".

You could call the smith who chambered the 223 AI and see if they have matched sizing dies, or fire form a few new pieces and send them off to have custom sizing die made. (Whidden for example). But that would likely only pay off if you were going through at least a barrel or two that are chambered with that exact reamer.

I'm a mechanical guy first not a metallurgist so I'm not fit to speculate on root causes. But at 20x firings I think I agree it's only about academic curiosity. I retire my brass somewhere between 10x and 15x firings.

David