Cartrige Case Ref. Info Update

[Fred Bohl]

The following data is offered for discussion and consideration. I'm not a expert in metallurgy or annealing so I'll refrain from interpreting the data. The cases were re-tested (post instrument calibration) and a Lapua "Blue Box" was added - note the difference from Lapua "Brown Box" 6mmBr.

 

[Taildrag15X]

Cartrige Case Ref. Info

Never thought to run them under the handheld XRF.....it's interesting that Lapua is the lowest in copper content.

 

[jonbearman]

Cartrige Case Ref. Info

Well that explains why the winchester lasts so long.But it is shocking that remington uses 80% copper. I am also shocked there is no tin on any of the cases.I didnt know zinc was such an important ingredient.Thanks for the imfo.

 

[jpretle]

Cartrige Case Ref. Info

Maybe some one w/ some expertise could explain the advantages or lack of advantages for the high/low copper/zinc content. Could one assume the copper is for case elasticity and zinc for strength?
Just trying to elicit some meaningful discussion.

 

[jpretle]

What??? No metalurgists here???

 

[Fred Bohl]

Cartridge Case Ref. Info Update

When I first posted this information and again when doing the update, I had hoped to elicit replies from expert metallurgists and to initiate a useful discussion. I've received some email responses and also some replies from experts from "back in the day" to messages that I sent soliciting there expert comments.

From those I have distilled the following consensus comments:

1. The range of Copper/Zinc ratios suitable for use in cartridge making by typical processes is 85/15 to 65/35 (% by weight or mass).

2. The range of Copper/Zinc ratios suitable for use in cartridges intended for reloading is 80/20 to 70/30. Above 80% copper, the resulting case would tend to be too soft and difficult to attain the distribution of hardness desired (harder at the base and softer at the neck). Below 70% copper the resulting case would tend to be too hard, work harden too quickly and require frequent annealing.

3. As the percentage of zinc increases, the tensile strength, yield strength and hardness tend to increase. However, above 35% zinc, while tensile strength will continue to tend to increase both yield strength and hardness will tend to begin to decrease.

4. The trace additives of iron and/or silicon are used to control the processing characteristics of the alloy. Trace additions of chromium will improve corrosion resistance and give a shinier surface (both largely cosmetic).

5. Selection of the alloy and additives is a trade off among: end use desired properties; processing time and yield; and cost of materials. For example, the classic 70/30 cartridge brass was considered an optimum combination of corrosion resistance and hardness for single use by the military with good process yield at acceptable material cost.

6. All of my responding experts were surprised by the brown box Lapua alloy except for the oldest. He remembered using an almost identical alloy late in WWII when copper was in very short supply for military small arms ammunition.

 

[jpretle]

Fred, thanks for that summation. Just the information I was hoping would come from your initial posting. Hopefully there will be more.
Thanks.

 

[kitsap]

Fred,

Outstanding information. Thank you for both the initial analysis and the summary of comments. Knowledge is always a good thing. Whether or not you like it or understand it is another question entirely.

Maybe there is a chance that Kevin Thomas from Lapua would shed some light on the subject.

DougF

 

[jonbearman]

Fantastic,now we can argue why norma is to soft considering it seems to be right in the sweet zone according to the figures.LOL

 

[300meter]

I would be curious to see the results of Lake City brass. Any chance of testing LC? The reason I ask, is that there is a great deal of this brass used for reloading and would be interesting to many of the forum members. Thanks for the results.

 

[memilanuk]

Very interesting the difference between the 'old' Lapua and the 'new' Lapua...

 

[johara1]

I can remember old Lake City 7.62 in the late 60's , i would neck them down to 243 in one pass. and turn around and neck them back up to 308 then up 358 and never a crack. I really think now it all has to do with cost not to make a better product.......jim

 

[FergusBailey]

At the risk of getting into another “unobtainium” discussion I would be really interested to see the Lapua 220 Russian old cardboard box compared to the new blue plastic box. The new blue box material seems to be significantly less resilient than the old brown box cases. When formed into 6PPC, the new Lapua seems to expand in the case head in about half the time than the old cardboard box 220 Russian brass.

I have hypothesised that with the significant increase in most resource costs in the last few years, that Lapua have chosen to remix their formula for .220 cases with more lower cost components to maintain the cost, rather than retain the old recipe and increase the cost. However this is just speculation on my part to explain observed results - a test like the above would be needed to draw any informed conclusion.

 

[Fred Bohl]

To those that have or will request testing of additional cartridges: We can and will try to accommodate a reasonable number of tests but please keep in mind that we are using very expensive equipment in the lab of a major corporation and the tests are being run by a volunteer on his own time.

Therefore I will ask that the person requesting the test provide the samples to be tested. We need to have two cartridges of each and they must be identified as to their history (new or fired), manufacturer, lot and/or year of manufacture at least. I will attempt to return the cartridge samples if provided with return address. Please also provide a valid email address.

Send samples to:

Fred Bohl
1156 Apple Blossom Drive
Neenah, WI 54956

 

[spclark]

I just ran across this thread & the test information you've made available to us. First I have to say thanks! Interesting information here.

Second, I'd like to ask if you're still accepting new samples of brass for testing? I have a few cases I'd like to submit for analysis if you have another session in the works.

 

[KevinThomas]

Sorry for the delay here, but been on the road a lot lately. We pointed this thread out to our QC folks in Finland, and asked them to do a review of the material used over the past few years; no change. we use (and have used) Cu-28%Zn, or typical cartridge brass that most in the industry use. As Pekka put it, it's hard to believe anyone is using anything significantly outside the 28-30% range, as that's pretty much industry standard.

 

[Fred Bohl]

Cartrige Case Ref. Info 2nd Update

Kent - thanks for the samples and see attached update.

SP Clark - yes, send the samples.

Relative to the post http://forum.accurateshooter.com/index.php/topic,3774122.msg35999733.html#msg35999733, all the test were run on a machine that has calibration certified traceable to NIST standards, each run includes an NIST certified reference specimen and was done by a technician with over 32 years experience. We have no axe to grind and no nefarious intent or profit motive. The data are good.

 

[lurcher]

I wonder are these %'s consistent across all calibers and do they vary batch to batch? Do other factors such as annealing at the factory have an impact on the way brass behaves?

People always comment that Norma brass is soft, yet it is only 2% more copper, is this enough to make a widely appreciable difference versus lapua?

People complain about remington brass but I always thought that this criticism was not directed at the softness of the brass but more the weight variation and general quality of manufacture?