Terminal work hardening of brass?

[thefitter]

I'm thinking that there must be a point that brass no longer work hardens any more.

I have recently noticed on some cases that I have reloaded well over a dozen times that the neck sizing and seating tension is extremely consistent.

Dare I say more consistent than new or annealed cases?

Thoughts? Opinions? Diatribes?

 

[nosualc]

I always thought it would work harden to the point of being brittle, at which point it would split.

Maybe not? I'm sure somebody here knows.

-nosualc

 

[jlow]

Yes, one reason to anneal is to reduce neck splits.

 

[BoydAllen]

I have some turned cases for my 6PPC that have been fired many times. I have never had a split, but they expand very little, compared to brass fired in a factory chamber, and are only sized a little to hold a bullet, with no expanding.

 

[fdshuster]

Have a large number of Lapua 220 Russian/6ppc brass that has been loaded 45+ times, never annealed & still perfectly usable. As Boyd said though, they are tight fitted necks , chamber neck dia. .262", loaded round neck dia. .260", using a .259" neck bushing die, turned neck walls are .0085".

Unlike the typical factory chamber with the very generous tolerances, these necks are being "worked" a total of .0015" per side. Makes all the difference in the world for brass life. Primer pockets remain tight.

 

[amlevin]

There's only one real answer to your question. A single word, "Depends".

Factory chamber or custom.

Sizing methods? Do you use too small a neck bushing then expand with either an expander ball in the die or a mandrel?

Far too many variables for a good answer as to how long the brass can be "worked". If you don't anneal, I guess that split necks are the best indicator that you've reached the limit.

Of course if you're like the shooter I watched Monday, his chamber is so tight he only resizes the necks about .001" each time. He's sized his chamber so the cases expand so little they don't really work harden .

 

[jlow]

Exactly!

 

[thefitter]

Sorry, what I mean is- is there a point were the brass no longer hardens anymore?

 

[BoydAllen]

Believe your experience. The problem often comes when we try to "explain" what is happening. Most of the time we don't have the proper tools to make an accurate determination of the exact mechanism that causes something, but we can accurately observe what happens when we do something.

I don't know why this happens, but I have observed the same thing that you mentioned in the post that started this thread.

Recently, a very experienced shooter and gunsmith told me that although he generally has found that using new (fire fireformed) brass for a match, gives the best results, that recently when he was having some unexplained fliers with new brasss, he switched to some very experienced brass and got much better results. I would say that you should believe the feel that you get when seating bullets, and your concentricity gauge. If they, with close attention to the first, tell you that your middle aged brass is doing well, then it really is. Of course the target is always your final arbitrator.

 

[necchi]

Sorry, what I mean is- is there a point were the brass no longer hardens anymore?

I don't think so, it will continue.

Brass cartridge cases aren't really 100% brass Copper. If they where then I believe that the matrix would become complete at a certain point and get no harder. Once the molecules where fully aligned that would be it, they'd be done.

But most cases are an alloy with only about 80% brass at best, the rest is zinc, iron, silicon and chromium. The act of firing and the resulting heat and pressure affects the alloy each time and if even a small amount of the other 20% metals where changed or removed then the current brass matrix would change.
The new mix (however tiny the change is) would cause the matrix to "reform again", (at each sizing) and each time become a different alloy of primarily brass,
The brass is forced to continue changing, it won't reach a point of stasis (a finished or complete hardening)
At some point, the alloy will loose enough of the other components, the brass matrix will become brittle enough to fatigue into a split neck.

Let's not forget the other problem with olde brass, Case Head Seperation.

(Next morning thought fix)
Point is, that brass is an alloy subject to all the things we put cartridges through as loaders and shooters, It's not just a Door Knob or fitting on a sail boat, a cartridge thats being used by a loader is in a constant state of change,,

 

[243winxb]

Not Olin>

modulus of elasticity- Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI
when work hardened. Modulus of Elasticity is 16,000,000 PSI. This means to pull a 1.000 inch long strip to 1.001 inch long induces a 16,000 PSI stress.
So if you pull a 1.000 inch strip to 1.005 inch long, you get about 76,000 PSI, which is the max obtainable.

My guess is - when the brass becomes work hardened & has to stretch more than .005" it cracks. On the chart 1 KSI = 1000 PSI. Olin > http://www.olinbrass.com/companies/fineweld/Literature/Documents/Alloy%20C260%20Data%20Sheet.pdf Olin's link gives lots of info, more than i know what to do with. ??? Bushing dies have given me the longest case life, avoiding neck splits in a factory chamber.

 

[amlevin]

Brass cartridge cases aren't really 100% brass. If they where then I believe that the matrix would become complete at a certain point and get no harder. Once the molecules where fully aligned that would be it, they'd be done.

But most cases are an alloy with only about 80% brass at best, the rest is zinc, iron, silicon and chromium.

I think you mis-typed here. A brass cartridge is 100% brass. The brass alloy itself is made up of those elements you mentioned as well a Copper. When all these elements are present in the same alloy, it's called "brass".

 

[necchi]

I think you mis-typed here.

DHOO!
Thank you,
I'll lay in the fix