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Measuring the "WEB" area of the case for pressure signs?

 
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  #8  
Old 12-04-2008, 02:02 AM
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Re: Measuring the "WEB" area of the case for pressure signs?

Some interesting reading for the OP:

http://www.shootingsoftware.com/ftp/...%2019%2004.pdf

If you want to read more articles on related topics, check out the Technical Articles section of RSI Shooting Software's site:

RSI Technical Articles
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  #9  
Old 12-04-2008, 02:57 AM
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Re: Measuring the "WEB" area of the case for pressure signs?

Over the years at Accurate Reloading forum I have endured hundreds for flame wars between Denton Bramwell "Denton" measure pressure advocate and Glenn Rice "Hot Core" measure brass advocate.

I think they are both electrical engineers, as am I.

After that much arguing, it is a stylized debate.

I have my own flow chart:
1) If I were to sell ammo, I would measure pressure* and develop
loads to SAAMI registered pressures.
2) If I am loading for a gun that is weaker than the brass, like a revolver with .040" thick chamber walls and a rimmed case, just don't exceed max loads in load books, where pressure was measured.
3) If I am loading for a gun stronger than the brass, load up to the threshold of short brass life, and reduce by at least a safety margin to find the max load for my gun.

* With CEA-O6-250UW-350 strain gauges and AD8554 op amps in an instrumentation amplifier configuration, I can get great accuracy in measuring the strain on barrel steel locally.
Instrumentation amplifier - Wikipedia, the free encyclopedia
One problem I have is the precision of where the gauge is epoxied onto the barrel.
Another problem I have is that the barrel is not a uniform thickness thin wall long tube. It is an open ended tapered tube. That gets me into Roark's book on stress vs stain on open ended tubes:
Amazon.com: Roark's Formulas for Stress and Strain: Warren Young, Richard Budynas: Books
I think Denton buys amplifiers, and calls mine "home brew", but mine are more accurate. The inaccuracy is in the epoxy, position, thickness, and formula for tapered open ended barrels. Then there is the error of value used for Young's Modulus for steel in the barrel.
I have a friend who has by passed this, and gone to pressure receiver and transducers.
That still leaves errors for the handloader, in that it misses the individuality of the gun and the error of the pressure registered with SAAMI.
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  #10  
Old 12-04-2008, 03:13 AM
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Re: Measuring the "WEB" area of the case for pressure signs?

Clark,

If a person didn't have the instrumentation and chose to go with measuring case head expansion... what would you consider a reasonable thresh hold to say 'No more'?

The reason I ask is this: a few years ago I had called Sierra tech support about one of their bullets (the new at the time 90gr .224 SMK), and took the opportunity to ask them why their published 'max' loads were so far below what seemed to be in relatively common use. To put it bluntly, why their loads seemed so pussified.

I expected the usual hemming and hawing about corporate lawyers and such, but what I got surprised me even more. The gentleman (don't recall the name) said they measured CHE with blade micrometers and when the case head expanded some specific amount (0.0010" rings a bell, but unfortunately I didn't write it down), that was it. Max load, period, based off expansion of the case head as measured in the extractor groove (to my understanding).

To say I was somewhat shocked that a major bullet manufacturer who publishes such an extensive loading manual was relying on such a low-tech and indirect method of pressure measurement would be an understatement. I are not an engineer (I just get to deal with the consequences of their work ) but that seems a little weird.

Monte
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  #11  
Old 12-04-2008, 04:01 AM
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Re: Measuring the "WEB" area of the case for pressure signs?

The Sierra rifle book is good, it stays the same for decades. I work up loads and come back down from problems and wind up close to their loads often enough.

They are nice to talk to or email.
I wrote them about the error in their pistol book that said that CZ52s were stronger than Tokarevs. I told that that it measures and calculates the other way. They wrote back that they just wrote what they read. That was refreshing to get the truth instead of a politically correct answer.

The Mauser case head used on a 308 is SAAMI rate for 62kpsi and is only good to 62kpsi.
The .222 case head used on a 223 is SAAMI rated at 52kpsi and is good to 72kpsi.

This is a problem for the 22-250.
It is manufactured with a slow twist barrel, only good for light bullets, but the .223 is practically as good with light bullets if both cartridges are loaded to the threshold of short brass life and backed off a safety margin.

The only niche for the 22-250 with advanced handloaders would be with a custom fast twist barrel.

But I will assume you have a stock rifle and only stock .223s have the twist rate to launch a 90 gr bullet with stability.

I would assume that Sierra was loading to 52kpsi, and not 72kpsi.
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  #12  
Old 12-05-2008, 09:44 AM
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Re: Measuring the "WEB" area of the case for pressure signs?

There is never going to be a standard, rule of thumb, or method that will apply appropriately across the board here.
Too many local factors..

It would be like predicting 'accuracy' from a barrel without having established a mountain of parameters and rigid definitions. Something that hasn't happened to date...

So if my load and dies produce a 5 reload case life to get best accuracy, and I can live with it, there is no problem. If I put alot of work into my brass, and need 20+ reloads from it, I'll watch growth very closely with my barrel, cartridge, chamber, brass, resultant ES and grouping, etc.
You cannot predict results here through procedure.

Just get to know your brass.
Look at each round pulled and learn what you can on the bench.
With this, you'll see that .0005" growth from a 223rem means something different than .0005" growth from a 6.5wssm.
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