There are two different measures of pressure, ie: CUP and PSI.My caliber has a max 64,000 psi what would the equilvelent be in CUP measurement?

There is no accurate and reliable "translation" available between CUP as defined by SAAMI procedures and psi. At the present, SAAMI still allows use of the old CUP pressure limits and procedures, but new cartridges are specified in terms of psi using the conformal piezo transducer.

If you caliber has a maximum average pressure of 64,000 psi, it is probably a modern caliber for which there is no CUP specification.

KenO

Ken,

Would it be correct to say that once you set a pressure limit in CUP, to get the pressure limit for that cartridge in psi, you have to take reference ammo for the specified pressure limit in CUP and then test with the piezo transducer to get the psi limit?

Jim,
Ken is of course right about there not being a straightforward conversion between the two pressure measurement systems. However, I'm remembering somebody on this site with a statistics background (denton?) has done an approximation of a translation based on cup and psi limit data for several cartridges and found a line or curve, within "reasonable" bounds of error (i.e., close enough for general informational/entertainment purposes rather than safety purposes). I believe the information was posted (or at least a link to the info was posted) within the last two years, so you may be able to find that data through the search function.

Edited to add link to previous discussion, which references a previous discussion with the data from denton.

CUP to PSI approximation

http://www.shootingsoftware.com/ftp/psicuparticle2.pdf

Read it carefully for the inherent limitations presented by the different measurement systems and the correlation between them.

First let me express a little bias. Having fired many rounds in barrels with dual instrumentation (CUP and psi), I do have slightly higher regard for CUP than for reading primers, case head expansion, bolt lift, and shiny spots. All are indicators of pressure, but I would not consider them to be reliable measurements of pressure.

The primary function of reference ammo is to establish the mythical "standard" or average barrel. Reference ammo is not an absolute standard of pressure, and lots typically are assessed at lower pressures that the specified max average pressures. If you do both CUP and psi measurement, the observed difference is applicable only to that lot of reference ammo. There are just too many other variables.

As I recall, Denton's work was based on comparing the two published tables of maximum average pressure, the old table expressed in CUP and the newer table in terms of psi. I don't consider that to be an accurate or reliable method of translation. SAAMI looked for a translation from CUP to psi for many years before they decided to generate a new psi table. If such a translation existed, I expect that they would have found it and would not have bothered with a new table just for psi.

We should respect the CUP system, play taps, salute it, and move on.

KenO

The Much Sharper Ken is (as usual) absolutely right.

What appears to be sloppiness on SAAMI's part is actually the inevitable limitation of an insurmountable problem � there's no known way to measure a sporting firearm's chamber pressure directly and precisely. The best that we can do is to measure certain related phenomena indirectly and conclude from those results what the actual pressure probably is.

The strain-gauge method in the Oehler "Personal Ballistics Laboratory," for example, dynamically measures the changes in resistance to an electric current through the strain gauge as the expansion of the barrel (under internal pressure) stretches the gauge. This system, then, measures one thing (the changes in an electric current] to indicate a second thing (the expansion of the barrel) to get an approximation of a third thing (the internal pressure that expands the barrel).

The gap in our knowledge is that we can only guess within a certain limited degree of accuracy how much pressure expands the barrel by a known, measurable amount.

The piezo crystal that SAAMI uses does essentially the same thing. It measures the changes in resistance to an electric current though the piezo crystal as a piston driven by chamber pressure compresses it. The same knowledge gap still limits us � we still don't know, and can only guess with limited precision, how much pressure causes the piston to compress the crystal by a measurable amount.

This situation is more beneficial to us than it may seem. Since we also have only a relatively vague idea of how much pressure to consider safe, we can not know where to scratch a narrow line in the sand or know how to march right up to it without risk. We have to observe a wider "warning track" that warns us that the edge of the cliff is near and try not to cross that "warning track" lest we run right off the edge of the cliff in the fog.

In the immortal words of Inspector "Dirty Harry" Callahan, "a man's gotta know his limitations" � and live within 'em.

edited to add:

The "copper units of pressure" (CUP) system was even less precise and far more limited and variable than either of the two systems that measure electrical resistance. In the old days, SAAMI called the "measurements" that they obtained by compressing a copper cylinder "pounds per square inch" (PSI or lb/sq in.) but in time came to realize that there was no way to know how much pressure actually compressed those copper slugs by a known, measurable amount.

Changing the terminology from "pounds per square inch" to "copper units of pressure" was a small step forward. Moving on to the electrical approximations was a larger step forward � and still short of perfect precision.

AMEN!

Good grief... this again?

Please take time to read and understand my article before reaching conclusions.

The basic mathematical argument is that any two measurement systems that are successful at measuring the same thing must be correlated and convertible. It is a mathematical impossibility for it to be otherwise. The posting format here at 24HC does not allow mathematical notation, but I would be happy to write out the very simple proof and email it to anyone who is curious. One result of my investigation is that practically all the deformation of the copper slug happens at peak pressure. So, both the piezoelectric method and the copper crusher method measure the same thing: Peak pressure.

Finding the conversion formula is not only possible, it is trivial. IIRC, from the moment the question entered my head (wondering how many PSI would be a reasonable maximum limit for my Swedish M96), until I had my answer, about 20 minutes elapsed.

After I published my findings, I was delighted to find that Dr. Lloyd Brownell of University of Michigan had preceded me by a few decades. In his landmark work on pressure factors, he includes not one, but two graphs for converting between CUP and PSI.

CIP, Europe's equivalent of SAAMI, has obviously been taking one set of measurements, and using a formula such as the one that I published, to convert from PSI to CUP. As nearly as I can determine, after analyzing their data, only two possibilities exist: 1) European instrumentation is a full order of magnitude better than US instrumentation, or 2) they are taking data in one system, and using a formula conversion for the other untis of measure. The second alternative is vastly more likely.

I can do it.
Dr. Lloyd Brownell could do it
CIP can do it.
Anything that happens must be possible. Since the conversion routinely happens, it must be possible. Furthermore, statistical analysis of the errors in the conversion indicate that the conversion is about as precise as our ability to measure pressure with the piezo method. It may not be perfect, but it is as good as the measurement system we are presently relying on.

All that said, there is one thing in the article that I wish I had done differently. In discussing the precision of the conversion, I developed the error distribution for converting single measurements from CUP to PSI. The question that usually comes up is different. The usual question is how to convert a specification. In that case, you get the benefit of multiple measurements, and the conversion is good to about plus or minus 1,000 PSI in the center of the curve, around 45 KPSI, and plus or minus 2,000 PSI near the ends, around 30 and 60 KPSI. If the question is how to convert between PSI and CUP specifications, what would you use for input except a table of equivalent specifications?

Note that the linear relationship is valid only for rifles, and only from about 28 KPSI to about 60 KPSI. We know that the actual relationship is curved, but within those bounds, a straight line is a good fit.

As noted by two contributors above, only The Almighty knows exactly how much pressure happens in the chamber of a firearm. The rest of us have to rely on methods of approximation. All approximations are lies. However, some of those lies are close enough to truth to be useful. So the key question is, how close to truth is the measurement likely to be? In the case of chamber pressure, CUP, piezo, and strain gauge measurements all provide some measure of useful information. Piezo and strain gauge measurements have the great advantage of producing output directly in useable engineering units. Both are capable of higher precision that the CUP method, but SAAMI has failed to exploit the full available precision of the piezo method.

The whole issue will soon be moot, anyway. CUP is clearly on its way out, and, eventually, PSI will be as well. Eventually, we will all shed our archaic measurement systems, and join the rest of the world in using more modern units of measure. Both PSI and CUP will be regarded as quaint historical footnotes.

I have read your article.

To the best of my knowledge, "CUP" is unique to SAAMI. CUP implies adherence to SAAMI procedures, not simply the use of a copper crusher element. From the appearance of Dr. Brownell's "conversion graph", it is apparent that he was probably referring to pressure measurements made in accordance with US military procedures. Did Dr. Brownell really refer to his copper measurements as CUP? Don't you wonder why your conversion algorithm is significantly different than Dr. Brownell's? The US military and SAAMI used different procedures and got different answers. The CIP procedures are different still. CIP's use of their formula to convert their copper procedure readings to piezo equivalent readings is appropriate. Incidentally, their formula is not quite linear, but close. All the "copper" procedures seem to give different answers.

I do not deny that CUP and psi measurements are correlated, but I regard correlation coefficients in the order of 0.9 to indicate only a correlation. It does not indicate that a measurement procedure should be be trusted or used. For comparison, I have been able to demonstrate correlations of 0.99 or even 0.999 between the SAAMI conformal piezo transducers, strain gages, and case-mouth piezo transducers used per NATO. I've been able to demonstrate correlation in the order of 0.98 between CIP copper and piezo transducer on a shot-by-shot basis.

Have you read and understand the SAAMI, CIP, US, and NATO procedures for pressure measurements using both copper and transducers?

Specifically, what procedure for measuring chamber pressure are your referring to when you say we will "join the rest of the world in using more modern units of measure"?

KenO

Good. I thank you for the courtesy.

You have also read Brownell, as I have. I would expect that from you.

Dr. Brownell learned his use of strain gauges from the same poeple I did, the Physical Measurements Group at Tektronix, and at about the same time. My job at that time was to be the regional Tektronix resource for physical measurements methods.

Most of my early published articles were in electronics, with more recent work in the statistics of measurement systems, designed experiments, and industrial processes.



Actually, no.

As nearly as I can read Brownell's Figure 14, page 35, I get the following, comparied with my model:

PSI............Brownell CUP......my model CUP

28,000.......28,000................31,100
40,000.......37,000................38,600
50,000.......44,000................44,900
60,000.......50,000................51,200

I would say that they track pretty closely, especially since Brownell identifies his graph as the "approximate relation".



Perhaps you are correct, but I am unable to find any such evidence within the article. His numbers appear to me to correspond directly to those you would get with the SAAMI CUP method.



You cannot make that evaluation on R^2 alone. But, FWIW, my R^2 of .937 corresponds to a correlation coefficient of .967.

This goes directly to the point I made about wishing I had written something a little different in my article. When the question is predicting one measurement from another, you have a valid point. When the question is converting one specification to another, the aggregation of the data reduces random error by the square root of N, giving a much better estimate than you can get for an individual point. The precision of the conversion formula is as I have stated: Good to plus or minus 1,000 PSI near the middle of the curve, and to plus or minus 2,000 PSI near the ends. Per the analysis I have done of the limited data I have available, this isn't much different from the magnitude of the random error in the piezo system, as applied by SAAMI.



Yes, very carefully. Wouldn't you expect that?

The CIP and NATO documents are not readily available to me in English. My familiarity with CIP methods is through what has been published in English on European reloading sites. If you have them in English, I would be grateful for a copy.



That speaks very well for careful technique, and a knowledge of what you are doing. Good work.

Now, turnabout is fair play: Have you read and understood any of the authors on formal measurement systems analysis? Wheeler? My own humble and obscure publications on the topic? If not, wouldn't it be appropriate for us to pool the knowledge we both have?

Almost forgot: The more modern system of measures I mentioned is the metric (SI) system of measures.

Again and again, I wish that Dr Brownell and my friend Homer Powley were alive (and still lucid!) to clarify something that Homer told me years ago.

Shortly before Dr Brownell died, Homer apprised him of basic errors in his approach to studying pressure factors. According to Homer, Dr Brownell then reexamined his work and conceded � graciously and gratefully � that Homer was right.

I've wished many times that I'd pursued that point with Homer. I have no idea what Dr Brownell's error[s] was [were], so his work has always been under an undefined cloud for me. Ignorance is Hell. Irresoluble curiosity makes it worse.

My impressions, for what they're worth �

The copper-crusher system was like a fisherman's rubber ruler � not accurate when stretched to its limit.

The piezo and strain-gauge systems are like surveyors' ropes � more nearly accurate but not when they sag noticeably in the middle.

We simply don't yet have a pressure-measurement system that approaches an accuracy level like that of a precision-etched machinists' stainless scale � which itself is more accurate at one temperature than others.

The rubber ruler's units of measurement correlate with the surveyors' ropes' units in different ways under different conditions.

+1.



Aye, there's the rub.

As nearly as I can determine, a single technician, working with the same piezo equipment, on the same day, and measuring ammunition from the same lot, can repeat a 10-shot pressure average within plus or minus about 1,000 PSI. Move it from lab to lab, and it gets nothing but worse.

Interesting, though understanding little of the theory and science, but some light shed into dense mind.

Any chance since measurements can be linear within perimeters, you guys are simply debating + and/or - of magnitudes at opposing ends of measurement - the rubber ruler, or variables? Did I understand that right?

The variables are what always got my attention, don't like to go there, unless VERY calculated.

Has anybody used Ken Howells' method of meausuring barrel pressure?

In a very gracious PM, our friend Denton tells me that this is incorrect:

He then explains:

I'm not about to quarrel with any of that! As I told him in my PM response, I just call 'em as I understand 'em as a layman, and what I posted was my admittedly correctable understanding. So now I'll let Den 'n' Ken hash it out. (But I still doubt that there's a useful way to relate CUP to lb/sq in., no matter how you "measure" the latter. Seems to me � outsider looking in � like comparing apples to algebra.)

I haven't. Don't even know what "Ken Howell's method" is. <img src="/ubbthreads/images/graemlins/confused.gif" alt="" /> <img src="/ubbthreads/images/graemlins/help.gif" alt="" />

In the attachment, there is a scatterplot of SAAMI CUP measurements vs. SAAMI PSI measurements.

You can put aside all the math, and interpret the plot this way: If it resembles a straight line, there is a conversion between the two. If it more resembles a shotgun splat, then there is not.

I'll go so far as to speculate why SAAMI has not succeeded in finding the relationship: I suppose they may have taken both CUP and PSI measurements off the same lot of ammunition. If you think about that for a minute, that is taking an infinitesmal slice out of the line, spanning perhaps a few hundred PSI on the horizontal axis. In that case, all you can see is measurement system noise, and you won't find a correlation. In order for the math to work, you have to span a range of pressures that is much larger than your measurement system random noise.

In the graphic, the red lines are the 95% Confidence Interval. We're 95% sure that the real regression line falls between them. The blue lines are projections of error. For each vertical blue line, the true value on the vertical axis lies between the two horizontal lines.

KenOehler, could you briefly describe for us how the CIP uses copper crushers and perhaps shed some light on why their crusher method better allows a simple conversion formula to piezo? I've wondered this ever since I first saw denton's plot of CIP copper and piezo numbers.

From denton's plot of SAAMI CUP and piezo, it was obvious something was quite different between the two copper systems. What is it about SAAMI's approach that creates greater variability than CIP's?

denton, I for one would be very happy to hear more about your investigation. I've read of two theories as to why crushers increasingly underestimate pressure as the true peak pressure rises. One is inertia effects. The other is a peculiar strain-rate property of materials, where very high rates of strain can alter the final deformation as compared to static (low rates) tests, a phenomenon I do not understand.

Hi, Karl!

Glad to see you here! Your web site is one of my favorites.

Karl, I admire the question, but don't have an answer. All I can say is that the high correlation between the PSI and CUP measurements indicates that practically all the deformation takes place at peak pressure... over the pressure range stated.

I'm aware that some measurements taken with very fast powders tend to more seriously underestimate pressure. Perhaps it has something to do with the rate of deformation.

I, uh, well, <img src="/ubbthreads/images/graemlins/blush.gif" alt="" /> I'm honored, sir.

A few new pages have been languishing on my PC for some time. I need to finish them. I also plan to add more Whelen excerpts, and I've just bought a copy of van Dyke's old book on still hunting, which I'll add over the next year (they are both in the public domain).

I truly regret my schedule in the U.S. did not leave me time to visit you, on my move from Australia to the U.K. I had talked with you about stopping by to get copies of some of Powley's manuscripts and then putting them on the web for others to enjoy. You've posted bits of them here over the years, and they are certainly worth getting out to the shooting world. I should move back to the U.S. next year, so hopefully I can stop by before next winter.

Karl

I just posted this in another Campfire forum:

2525 --
You just asked a most intelligent question.


The CIP and old US military test procedures required that a hole be drilled in the case immediately below the piston that squeezes the crusher. The SAAMI procedures either placed the piston hole at the casemouth or allowed the pressure (at approximately 20K psi) to rupture the side of the case under the piston. In the case of CIP or the US military, the crusher was subjected to a gradual application of force as the powder ignited. Speeds of the piston were relatively slow and the response of the crusher was substantially independent of the powder burning rates. Inertia of the piston was also insignificant because accellerations were small. Using the SAAMI procedure of either blowing a hole in the side of the case, or suddenly exposing the base of the piston at the casemouth to high pressure gas, the piston inertia and velocities are very significant. It is like hitting a crusher with a ball peen hammer instead of squeezing it slowly. The crusher response may overshoot or undershoot depending on pressure level, burning rate, and the pressure at which the case ruptures.

No, and I extend my apologies to Denton, I have not read all the CIP procedures (they are in French). Approximately 20 years ago I did spend a week at the Belgian Proofhouse where the Proofmaster, the chairman of CIP, the European rep for the piezo transducers, and I spent five full days at the pressure gun firing simultaneous tests with their copper procedures and the conformal piezo transducer. (We had special barrels for each caliber set up with dual instrumentation so that we knew we were measuring the same pressure with the two procedures. We fired a wide variety of ammo and pressures with each caliber.) It is my understanding that the data we collected back then forms the basis of their equations relating their copper measurement to their piezo measurements. Their formula is similar to the graphs I remember from Dr. Brownell's work. (I'm working from memory, I actually haven't seen either in many years.) That should be no surprise since their procedures are similar to those used by the US military.

If you do not recognize and understand the different procedures for using copper crushers to estimate pressure, you can just as well ignore all copper crusher numbers. I cannot understand why any modern handloader is truly interested in copper crusher values for pressure unless he is seeking justification to increase the pressures of his own loads. For instance, the max allowed CUP value for 357 Mag is 45,000, while the max allowed transducer value is 35,000 psi.

Incidentally, Denton's relationship predicts a psi value of 50,200 instead of 35,000 for the 357 Mag. To his credit, Denton's paper restricts his equation to rifles, but the SAAMI procedures still use the same crushers and undrilled case. (And I don't know of any SAAMI member who has used crushers on the 357 Mag in decades.) Perhaps the crusher is smart enought to read the headstamp.

As I said before. Don't try to make CUP something it is not -- play taps, salute, and move on. I don't want to rely on it or defend it.

Denton's relationship makes no prediction at all for the 357.

If your relationship makes no prediction for the 357 Mag, how about the 44 Rem Mag? SAAMI Centerfire Rifle Standards show 40,000 CUP and 36,000 psi for this cartridge. Does not your relationship show approximately 42,700 psi? If it is not considered a rifle cartridge, why is it in the SAAMI rifle book? Even the 223 Rem shows 52,000 CUP and 55,000 psi in the SAAMI book while your relationship shows 60,900 psi. Perhaps you are not concerned by a 10 - 15% difference, but I am.

KenO

Thank you, KenOehler, for the insights. The problems resulting from case rupture in the modern SAAMI tests are easy to understand. One piece of the puzzle in my mind remains missing, though. Why does a crusher increasingly under-indicate pressures as the true peak pressures rise? Is it this mysterious strain-rate property of metals that I've read of?

You wondered why anyone today would be interested in the true pressures indicated by some old crusher rating. Speaking only for myself, it had to do with my interest in older single shot rifles. Many of the classic designs disappeared before piezo systems were developed, and I've long wondered what stresses those old guns were actually taking. Unfortunately, there seems to have been many different crusher arrangements used over the years, and I had already come to the conclusion it's just not possible to correlate a crusher reading in 1910 to one in 1935 or to one today.

Also, a few years back I got to playing with a Powley Computer, which was developed with crusher readings. At it's core, Powley's calculations use basic physics, and at first thought, it appeared there must be some decent correlation between crusher and true pressure; and I went to learn more about crushers. I later decided the errors the calculations sometimes give were not due to crusher effects, but to the necessary simplifications a slide rule device must employ for a problem such as this.

Regardless, I still follow the topic whenever it pops up. (I also pay money to ride behind a steam locomotive.)

I'll finish by throwing in an observation on the .357 you brought up. Some labs, such as at Western Powders, use only piezo, and others, such as Hodgdon, still use their older crusher set ups. There seems to be a trend that loads developed in CUP for the .357 outperform those developed in piezo. If so, this suggests that the true pressure in the CUP loads are higher than those in the piezo loads. In other words, the .357 ratings may not be quite the anomaly indicated.

So, it seems I've brought up Yet Another Question: how did SAAMI establish piezo ratings for those cartridges which already had a crusher rating? I've always assumed they fired various loads (bullet weights and powder speeds, etc.) with both systems and after looking at all the scatter in the data, assigned a piezo pressure they felt either representative or at least not likely to cause troubles.

KenO (I appreciate the change to differentiate between you and Ken Howell) has asked a question I would like to hear an answer to also. Of course, I shoot .357 Mag in a Handi rifle, so the same situation should exist as with the .44 Mag.

As an observation, it doesn't seem like the industry has had much of a problem converting LUP to PSI, even though they (shotshells) use much the same powders that handguns use. In 1970, DuPont posted a 1 1/8 ounce load of 17.0 gr of 700X in a AA hull and a WAA12 shot cup as 1140 fps at 9,600 psi. In April 2004, IMR posted a 1 1/8 ounce 17.5 gr 700X load, with AA hull and WAA12 shot cup at 1200 fps and 11,300 psi. If you consider the extra .5 gr of powder used in 2004, it's pretty consistent with load and data from 34 years earlier.

It's items like this that makes one think, "there's something rotten in Denmark"! <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

Classifying the 357 and 44 is RIFLE cartridges? I may be off on this, but I do believe they were designed as revolver cartridges, and that most people use them that way. At least where I do my shooting. As I have said from the beginning, I did not study cartridges that were designed for handguns, and they are outside the inference space of my model.

If you'll print the graph I posted, and follow the procedure that I outlined for estimating 95% error points on the vertical axis for an input value of 30,000 CUP, you'll find that the model predicts a fairly large error in that region. So there is no surprise there. When you give someone an estimate, you also owe them a statement about the precision of the estimate. I've done that, and cheerfully told the world how great I think the error is down on the extreme lower portion of the graph. That's one reason I restricted my statement.

Yes, the 223 is a peculiarity. If you've read my article, you already know that I identfied it as such. Its residual is large, and that means that for some reason probably lost forever, someone did something significantly different in asssigning the PSI and CUP upper limits for that cartridge. I identified it as something I couldn't explain, and went on to explain what I could.

In any event, the important but subtle distinction that you have to make is the difference between a Prediction Interval, estimating where individual points will fall, and a Confidence Interval, predicting where the aggregated line is. The latter is usually the question of interest, since that is how you convert a specification. You seem to be stuck on looking at the individual deviations, which relate more to Prediction Intervals, and desperate to find examples the model was never intended to include. Why the obvious angst?

The glass is half full. We don't know all things, but we do know some things.

Maybe someday, I'll get around to building a more general model, and the glass will be completely full. But probably not, since I have long since answered my initial question, which was, how many PSI can I safely run in my Swedish M96?

Here's another little old observation, just to complicate the discussion further without offering any hope of resolving anything � Homer told me many years ago of one SAAMI member who was using and reusing the same copper crushers over and over again in the pressure gun, presumably in different pressure barrels. His emphatic implication was that the "pressure" numbers in that SAAMI member's data were entirely untrustworthy even in the old CUP days.

So I'm in KenO's camp, with one wee exception � we're 'way past "Taps" and far into the years of replacing the wilted flowers on CUP's grave.

Ewwww! Yuck! Egad!!!!!



Yup. Alas poor CUP, I knew him well....

Anybody here yearning to see a product test on a buggy whip? <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

Ken,

I suppose the Old Order Amish would be interested in buggy whips, since they still use them, daily. They use guns too. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

Denton, perhaps you should have quoted the next line, too:

'A fellow of infinite jest ...' <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

� and how many, d'you s'pose, log onto 24hourcampfire.com and read Smokelore, huh? <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

Their loss!

Well,the more I keep learning the less I know.It won't be but a few months and I'm going back to a bow and arrow.

This was (is) a geat thread in that the information comes from such authority.When all is boiled down,it doesn't matter if there is relationship between CUP and PSI,because not one of the posters thinks that CUP is a standard of record.The thing that amazes me is that there is NO finite way to measure chamber pressure ! The more I know the less I understand.

I was just reading last night about PCB's conformal piezo setup and was wondering, why in the world that wasn't the first approach? Any time the physical characteristics are changed, i.e. drilling holes or using gas ports, the data becomes less than ideal. And yet, that was/is the SOP for many of the systems utilized.

The really interesting thing is the ability to more or less calibrate the instrument with hydraulic pressure using the conformal method, in the actual test barrel/receiver.

Here is the 1999 article on conformal sensor measurement I forgot to include above.
http://archives.sensorsmag.com/articles/0599/0599_p93/main.shtml

Another interesting read is this one.
http://www.fas.org/sgp/othergov/doe/lanl/lib-www/la-pubs/00329005.pdf
It's about the Trinity atomic test on July 16, 1945 that used a series of .1240" copper crusher balls to measure the pressure of the explosion. The reported variation in calibration, from the California Institute of Technology, was "about 30 fps" and "The calibration curve obtained was found to be a straight line with a slope of 238 psi/mil compression."

This data was collected less than a month prior to the release of the two bombs over Japan, in August 1945. The first bomb dropped was a U235 bomb, but the second was a Pu239 bomb, from a man made element. Glenn Seaborg discovered Pu239 in 1941 and the initial samples available to the Manhattan Project were measured in micrograms. There are 453,592,370 (or 4.5359237 x 10^8) micrograms in 1 pound. Measurements like that make 6.0 x10^4 psi pale in comparison and that ability for precision measurement existed in 1941 or before.

My point in all of this is, the copper crusher, contrary to the opinions of some, is capable of precision and as Cal Tech noted, it's scale is "a straight line". When I quoted the UK's National Physical Laboratory as using "calculation of distortion effects at higher pressures (from the elastic properties of the piston-cylinder materials and use of finite element analysis techniques)" as a standard, instead of piezo electrics, that should have provided a clue that distortion effects are more precise than electrical impulses. There is nothing wrong with the system/methodology utilizing copper crusher, it's the specific application that is flawed. It appears that some of the flaw of copper crusher utilization in ballistics has been repeated in the use of the piezo electric.

It's a very simple principle. You can't alter what you're testing, because if you do, you aren't testing what you're testing. It's different from the original and things that are different aren't the same.

If the copper crusher approach can yield a stright line but fails to correlate with another system that yields a straight line - psi - then we're left with a few possibiities. First, we could be measuring different phenomena - possible, since we all seem to agree we're not measuring "pressure," per se, but rather the effects of physical distortions. Second, and more likely, we're seeing the effects of varying protocols.

I am concerned about, and don't understand, the references to "bury the copper crusher" method. I shoot several calibers, including the 6.5x55, for which only the copper crusher pressure data is available. Perhaps I missed the point, but if I want to increase the pressure of those rounds in my up-to-date rifles, what options do I have but to seek a conversion from one method to another? (That's an honest question - not a diatribe, by the way.)

Jaywalker

A switch to the conformal method is probably a step in the right direction of actually determining the pressure of a cartridge. The case becomes a diaphram that acuates the piston directly coupled to the sensor. There is no drilling, gas ports or cases blowing out that alters the burn rate and/or volume the gases expand into.

It can be calibrated with a known hydraulic pressure and has a long life span that alleviates the need for changing instruments during a long string of testing.

The degree of accuracy should be sufficient for real world application of the data obtained, since it's apparently the same piezo presently utilized with a different protocol.

The elastic properties of the actuating piston can be compensated for during the calibration process.

The speed of pressure build up and the operating temperature may present problems, but no more so than the system(s) presently employed.

Cartridges that are copper crusher rated and known to function without problems, can be tested and a baseline in actual pressure can be established.

Implementation would probably depend on the industry's acceptance and willingness to finance the switch over.

I faced the same problem. I have a milsurp Swede, and a modern FN action with a Pac-Nor barrel. That's why I started the whole conversion thing in the first place. I developed a conversion from SAAMI CUP to PSI, and also from CIP PSI to SAAMI PSI (they aren't the same). Both methods gave me close to the same answer, and life is good.

For the modern action, I simply chose the 30-06 limit as my 6.5x55 limit. That's a fairly conservative choice, since other cartridges with the same case run higher pressure. Even so, I was safely doing 3075 fps with a 120 grain bullet, but decided to throttle back about a grain.

Measurement systems usually have an element of random error in them. Both the piezo and crusher methods are prime examples. In a system with abundant random noise, you can still get any level of precision you want, by averaging (to get an aggregated value). It's just a matter of how many samples you have the time and patience to collect. If I remember the data correctly, the standard deviation of the random noise in the crusher method (one technician, one system, one day, one lot of ammunition, i.e., best case) runs around 1800 PSI. So, 95% of the time, individual shots are going to fall between plus and minus 3600 PSI of the mean value.... quite a range. However, we average 10 shots, and that pulls the error down by a factor of the square root of 10, or something about 1150 PSI or so. That may sound like a lot of error, but it is actually satisfactorily precise, assuming nobody is doing the naughty things Ken described.

The piezo method data that I was able to get had a real live trend in it, indicating a major uncontrolled variable. Lumping that trend in, the standard deviation of the error in the piezo system is more like 1350 PSI. Regressing the systematic error out gets the piezo system down around 450 PSI for a standard deviation. In that case, a 10-shot average would give precision down in the 300-ish PSI range, 95% of the time, assuming someone took the time to track down and eliminate the systematic error. Otherwise, the piezo method is only a little more precise than the crusher method.

So, the piezo system is fundamentally capable of much less random error than the old CUP system (higher precision). It's easier to apply, it gives numbers in real engineering units, and it gives pressure as a function of time, where the copper crusher method only estimates peak value.

To get best case piezo precision from the CUP system, you'd have to average about 90 rounds.

But can we assume that?

If one rut on the road to Hell is Good Intentions, the other has to be Assumptions.

Homer Powley lamented the fact that none of the SAAMI members (several of whom he worked with, as a consultant) was willing to pay the full-time salary of a really-O truly-O ballistician (a name plate on his desk that says "Ballistician" doesn't make any man a ballistician), and one of my SAAMI friends (a "ballistician," according to the company's organization chart) emphatically confirmed Homer's statement that no SAAMI member employed a truly qualified professional ballistician. (The very capable ladies who operated the pressure guns were operators � not even technicians � knew little or nothing of the critical principles involved, and had no one there to tell 'em.)

Knowing that at least one SAAMI member's data came from reused crushers, and that no member employs a qualified professional ballistician, can we assume that all else is squeaky clean in the SAAMI CUPboard? Or is it wiser to distrust all CUP data from SAAMI, new or old?

Trust whatever seems to confirm your conjectures and theories if you like, but I don't even take fresh flowers to CUP's grave any more.

And since the brass cartridge case is the limiting factor, I consider any cartridge with a .30-06ish head to be capable of safely withstanding the same peak pressures � no matter what old SAAMI or CIP specs, CUP data, tea leaves, or Tarot cards may say.

The first .444 Marlin cases came from the same line of blanked cups that made the same company's .30-06 cases � precisely the same brass, diverted from the .30-06 line and finished with different final configuration and physical dimensions. That may not be the practice now, but I rest in the confidence that no company specifies x-strength brass strip for their .270 Winchester cases and weaker brass strip for their .25 or .30 Remington cases.

I know! We'll have KenOehler rig up a conformal piston with crushers! Damn those electrons anyway. <img src="/ubbthreads/images/graemlins/wink.gif" alt="" />

(Now, if we can just get the average thermal efficiency of a steam locomotive above 3%...)

Ken,

You've given information that is probably very carefully kept within the industry.

We've been shooting the .30-06 with an amazing assortment of powders for 100 years and the vast majority was worked up with the CUP system. The only notable problem was a handful of 1903s with questionable heat treating.

I too have serious reservations about the economic feasibility of stocking numerous grades of cartridge brass. We live in an age of "one size fits all" and I feel cartridge brass is no exception. It's all probably made from Olin C260, or a comparable alloy, hardened to stand 89,000 psi or more. (Isn't it amazing that Olin knows and publishes the actual psi pressure the brass will stand?)

2525, it isn't the electrons that are at fault. They seem to be remarkably stable, since I don't remember ever hearing of a stockpile of depleted electrons existing. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

I'm still trying to understand the objections to a CUP/PSI conversion, and, unfortunately, the references to CUP burials etc. seem to be impeding my understanding. Is it your belief that cartridges whose max loads were developed under CUP criteria should not be exceeded? If that's not your meaning, can you please explain what you do mean? Since that seems unnecessarily restrictive when it comes to the 6.5x55, for instance, I have no doubt I've misunderstood you.

If I'm mistaken, how would you recommend we set a limit on velocity or pressure for a cartridge whose capabilities have been constrained not by brass limits, but by that of old rifles we don't own?

Jaywalker

One fall, our division's secretary came around asking everyone to set dates for the coming year's vacations.

"I don't know yet," I said. "That's too far ahead for me to plan for, right now."

"Just give me some dates. We have to know when you're going to take your vacation."

"But I don't want to commit myself to dates that may not be right for us."

"Oh, you can change 'em, any time you want to. You won't have to commit yourself to those dates."

"If I won't have to commit myself to those dates, what good is it to list some now?"

"Well, we have to know."

"What will you know now, if I won't have to commit myself to 'em and can change 'em at any time?"

"Why are you the only one who's giving me a hard time?"

Manifestly not. <img src="/ubbthreads/images/graemlins/grin.gif" alt="" />

Ken Howell.

Re: Vacation Schedule

You're a very diplomatic silver-tongued devil. Well said.

KenO

Looks good to start with, but at near 29,500 psi the thickness is down to 0.001 inch. The linearity can't continue much farther.



Can't argue with that, but it does illustrate a problem with using drilled cases.

KenO

Jaywalker,

The industry has set their pressure specs, but just like the vacation schedule, it isn't a real commitment. It can change at any time and probably will.

You can't count on the old loads, unless you have powder from that era, because they can and do change, notably the surplus powders and DuPont/IMR powders.

The bottom line is, the reloading manuals are a guideline that will give you a safe load for a gun of the appropriate chambering. After that, you're on your own. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

Now, I'm fixin' to go load some H-375 that has been discontinued for 40 years or more and has very scarce data.

KenO, I hope the hunting is better close to Luckenbach than it has been here! Here's a deer taken just a little north of you, around 1955.

That reminds me of a lecture on economics I attended at Caterpillar. One of the company's top economists was telling our class of newly hired engineers how important the company's 5 year economic outlook was for planning business strategy. One of the other engineers asked the obvious, namely, how accurate had the five year forecasts proven over the last 20 or so years. The answer amounted to: the forecasts were worthless, but management needed something to plan for, regardless.

I just shot coffee through my nose.....


Is there any chance you would PM me your web address that was refered to earlier? I would enjoy having a read.

Sorry about the coffee. You can find the address in my user profile, but I fear you'll be disappointed.

Re Ken Howell's Vacation Schedule: Ah, now I understand your death of CUP. As some primitives would have it, death comes in several stages: "dead," "dead all over," and "dead forever." Your vacation schedule as a topic was dead, but could eventually recover and become whole. Or possibly, metaphorically dead, as in "improper to discuss."

Sorry, I don't think it's "well-said" at all - it's merely avoidance. You have commented that CUP is dead, while that is manifestly untrue; I have several current reloading manuals that list CUP levels. As long as we still have to use it, CUP is not "dead forever."

Jaywalker

thanx for the response...

somehow I doubt it (disappointment).

I don't put any stock in horoscopes or ancient but still published folk lore about unicorns. Don't have to use either one. Neither is reliable, even for the superstitious and gullible. And neither is intentionally misleading. I don't buy the notion that currency of publication by misleaders and the misled carries any obligation to respect, to use, or to rely on.

When my kids were little, I used to watch cartoons with 'em (the road-runner and the coyote were favorites). After some of the more outlandish escapades, I'd solemnly pronounce that I didn't believe that any of that had really happened.

"Aw, Daddy! It's a cartoon!"

Right!

Thank you, yes, that is more clear than your previously entertaining but obscure comments on the death of CUP. I am answered.

Jaywalker

Lead and copper crushers, transducers, and strain gauges all help to define � very vaguely � broad regions of safety and peril, with very wide and very hazily defined zones of demarcation between these regions. The demarcation zones that the lead units (LUP) "define" are wider and hazier than those "defined" by the copper units (CUP), and both of these are wider and hazier than those "defined" by the electrical systems, which are actually wider and hazier than their numbers imply.

Even if we were to adopt new terms like "transducer units of pressure (TUP)" and "strain-gauge units of pressure (SGUP)," we'd still be kidding ourselves. We'd be wiser to think in terms like "copper regions of safety (CRS)" and "instrumental regions of safety (IRS)."

We delude ourselves when we try
(a) to assign units of measure (implying precision) to these regions,
(b) to equate these units with pressure (force per square inch),
and
(c) to assign narrow demarcation lines between "safe" and "dangerous" to cases and breeches.

In our obsession for precision, we're trying to apply micrometers to the observable but immeasurable � like trying to mike love to the nearest fraction of � what?

I would disagree that we're always deluding ourselves. Those who report that their load develops "64,189 psi" are deluded, but those that report "about 64 ksi" may not. Engineers long ago adopted the convention that you only use as many digits as you have confidence in, and as you've correctly pointed out, even two digits is debatable.

The correct units are indeed "psi", but we simply cannot measure such transient high pressures with that degree of precision we take for granted today. Decades ago, William Davis made the argument that units of "CUP" are rather annoying, and that the correct units are actually "psi". The problem is the deluded fail to consider the measurement method. While crushers do indicate in psi, the method is not able to track true peak cartridge pressure to even 1 digit at high pressures. I rather like Davis's suggestion to use "psi-copper".

It's all in the name I suppose. The point you've made is that this is a very difficult measurement, and that we should always remain aware of our limitations.

Your comments on the grayness of lines between safe and not-safe are, I think, very well taken.

Oh, I know that many do and will disagree.

That's life.

That's human nature.

Habits clothe not only nuns.

Ken,

I know my opinion will do nothing for your self image, but I think you've done a very good job of putting things in their proper perspective!

Let me voice yet another view of the elephant:

Even if a measurement system lacks precision, it is adequate if it gives you enough information to make a proper decision. The place people tend to get in trouble is when they assume that the measurement system is error free, when it is not. Hence the need to characterize the mean and standard deviation of the random error in a system.

The tradition in engineering is, as said, to only express as many significant digits as you know. Unfortunately, there is a downside to that, once you look at the statistics. Truncating, or rounding, introduces random error of its own. If you're reporting to the nearest 100 PSI, you're introducing roughly an additional 33 PSI of random error. If you report to the nearest 1,000 PSI, you've added about 333 PSI. For the sake of that problem, I'll generally report as 55.6 KPSI, even though I only trust the measurement to two significant digits--I can detect 333 PSI on some days. On other days, I'll forget that other people aren't as nutty as I am, and just give all the digits. Of course, that sometimes leads to problems.

For a hunting-book publisher, I edited a Danish writer's manuscript that frequently mentioned the elevations where he was hunting and prominent near-by land-marks � in meters. I calculated the equivalents, of course, but had to finagle 'em a bit to avoid false "precision."

The publisher's style called for this format � "20,320 feet (6,194 meters)" (which some here are sure to recognize as the elevation of Mt McKinley, now renamed "Denali"). The manuscript would have in its stead "6,200 metres." If I'd gone with the strict, precise equivalent of "6,200 metres," I'd use the misleading and inaccurate form "20,341.166 � 7 feet (6,200 meters)."

So the American book, as I edited it, would read instead for that elevation "20,320 feet (6,200 meters)" � a bow to imprecise custom to avoid imprecision in specifying topographic elevation.

Reason? Europeans list elevations in whole meters, not fractions of meters, and Americans list elevations in feet, not fractions of feet. Listing precise equivalents of either would lead to misleading, illusory, false "precision" in the other.

I asked earlier if anyone on this thread had used Ken Howells' method of determining barrel pressure to which the Ken Howell on this forum denied any knowledge of so reckon my wires were crossed. Sorry, Ken.

What I have before me is a 36 step formula that was copyrighted by a Dr. Ken Howell in 1996. Says it was adapted by the author from his book in progress, Loading and Testing Custom Cartridges and used here by special arrangement. Line 36, I think, is peak pressure in PSI.

Anybody know anything about this? If so, how does it compare with todays' method of determining barrel pressure?

Calling it "Ken Howell's method" without any further ID threw me. That's not my method. It's Homer Powley's. I don't have that old article close at hand to check it � doesn't it say that it's Homer's method? And to be precise, I didn't copyright the method � I copyrighted my article about it.

That's a method of estimating pressure � doesn't claim to be a way of measuring pressure � so is a fairly reliable way of approximating it. More reliable, at least, than miking case rims or looking for tell-tale warnings in the ease or difficulty of opening the bolt, etc.

There's a typo in my original article, later corrected. But it's in the work table's example figures, so it doesn't affect the rest of the procedure.

I have no way of knowing how many people besides Homer Powley used this method of estimating pressure.

Ken, your name is the only one on this page and the way it is worded, your copyright is on the formula itself. My terminology was DETERMINING barrel pressure but your post says ESTIMATING which , I'm sure, is the better word. Sorta like one guy says the world is round but someone else says it's oblong. <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />

But my question is have you or anyone you know ever tried this formula against the modern devices available? Certainly
this method is much cheaper to use, but is it close enough to count on?

My thoughts are that what is available now still is not 100% correct as such variables as barrel material and thickness would make a difference in readings. Maybe so; maybe not.

I would appreciate your thoughts.

Thanks

I've found Powley's formula for estimating chamber pressure to be of some use, but it can badly underestimate pressure. A few notes on it can be found here. It should be used only for normal charges; if you try 4198 in a cartridge best loaded with 4350, the pressure estimation won't be close. It also has some problems with low SD bullets in relatively large cases. Used "in reverse," so to speak, the formula is useful for predicting the performance of new cartridges.

Thanks,2525

That is a whole lot of information! Much more than be ingested by me, I think.

It's a good thing that some people have the understanding and time to research these things.

Thanks again

Ivan

I didn't read every word on your referenced site, but didn't seem to notice any references to the difference in density for IMR powders.

Recently I weighed a case full of DuPont IMR 4831, struck off level with the mouth, in Rem 6mm brass at 48.1 gr. The manufacture date of that powder was around 1974. I then weighed some IMR IMR 4831, made around 2003, from the same piece of brass and got 52.7 gr. The DuPont powder was US manufacture and the IMR was Canadian manufacture.

Obviously, Powley didn't use IMR 4831 in his 1960s calculations, since it wasn't produced for the public until the 1970s. However, based on loads of 4350 we used in the middle '60s, the same situation exists with it (a full case load of '60s powder is less than a full case now).

How has this affected the calculations or has it even been considered?

Powley's equations predict a charge weight, not a volume. I'm not aware that the chemical energy per gn has greatly changed, and the energy per gn is what Powley would have been counting on in his performance calculations. What you report is that modern IMR powders pack more densely. Compared to Powley's assumptions, this would leave the case with more air space in it, something I think he hoped to avoid, if only to get more consistent ignition. If this greater density is true across the IMR line, a Powley today would want to increase the loading density a bit, up the performance predictions slightly, and slow down the recommended burning speed a smidge. Of course today, with digital computers readily available, we now have QuickLOAD, which can carry out more detailed calculations.

The copy of the equations I used in this version were taken from an NRA book published in the early 80's. It would have been a simple matter for either Powley or Davis to add 4831 at that time. However, I recall 4831 had been developed in WW-II and that Hodgdon sold the stuff surplus, so Powley would have known about its properties, even circa 1960. Indeed, the originals also predict charges for an old, extra slow IMR military powder no longer available.

Homer � and possibly Bill Davis � considered the surplus powders "junkyard stuff" and didn't think that it was consistent enough to be included with the commercially available (more rigidly controlled?) IMR powders. Homer and Bill worked together at Frankford Arsenal, so they knew some intimate details about powders that weren't public knowledge.

IMR canister powders were blended lots of tested individual batches, blended to make them fairly consistent from lot to lot, and identified by lot numbers. Surplus powders, by comparison, were essentially "anonymous" in respect to lots and batches by the time when they were repackaged in bags, canisters, and kegs in Kansas. And Bruce Hodgdon was not at that time equipped to test them as DuPont tested its batches and lots.

Homer had far more respect for the consistency of the IMR powders than he had for any other maker's powders, because of the ways that DuPont tested the batches and blended them into lots.

Ken, for some time I've been curious about the equation Davis gives for powder selection index. This is not the same equation as used in the slide rules. Do you know if it was Davis or Powley who made the adjustment? The version given by Davis is much more accurate. I've assumed it was Powley who made the correction, but Davis is a pretty sharp fellow as well. I really liked that reloading book Davis did for the NRA. It's a pity the NRA didn't keep it going.

Homer's original equation for the little slide rule was designed around a peak pressure of what was then thought to be about 45,000 lb/sq in. Slippage in the production of the device raised that figure to about 47,500 Whatevers in the results that it produced. Homer figured that was close enough for his purposes and let it go at that as far as the "Powley computer" was concerned. But he never (IIRC) stopped testing and tweaking his equation and sharing those minute tweaks with his friends � including, for sure and certain, Bill Davis.

Incidentally, Homer was one of the first figgerers to set himself up with a TRS 80 computer. He learned to write BASIC programs for it � which he also shared with his friends. And it was the computer still in service on his desk when he died in 1999. I never could get him seriously interested in anything more powerful.

edited to add:

I think he'd be in Hawg Heaven today with XP Professional and QuickLOAD.

For some reason, the Hodgdon vs IMR account just doesn't seem right. Speer #7, which is what I used then, listed 50.0 gr of 4831 as the max load in 6mm Rem with 75, 80 and 90 gr bullets. Obviously, all you can fit in a case without using a drop tube. Since IMR 4831 didn't even exist when it was published, it has to be H4831 they were using. Not knowing the difference between the two powders in the early 1970s, I tried to get 50.0 gr of IMR 4831 in a case, but 48.0 gr was all that would fit and my notes reflect that fact.

Not having the data easily at hand, I went out and weighed some more powder, all in the same 6mm Rem case, struck off level.

H4831SC 53.5 gr
DuPont IMR 4831 48.4 gr (1974 lot)
IMR IMR 4831 52.3 gr (2003 lot)
DuPont IMR 3031 47.2 gr (1973 lot)
IMR IMR 3031 49.7 gr (2003 lot)

The only IMR 4350 I have is a 1981 lot, that was made in Canada, and a recent lot, also made in Canada. The SR 4756 I have from around 1983 is also Canadian made. That indicates the Canadian made powder, with possibly a different density, has been around since the early 1980s.

Ken Howell ---

Just as a matter of curiosity, did Powley's pressure units refer to what Bill Davis would call "psi-copper" or to what SAAMI would call "CUP". Given that both Powley and Davis had backgrounds in US military testing, I would suspect that both would use the "psi-copper" mindset, and that both would consider that the cases should properly be drilled prior to firing with a crusher. On the other hand "CUP" implies to me the use of the SAAMI procedure where the case is not drilled. Response of the crusher can be significantly different with the two different test protocols.

Considering that Powley evidently did his work on his slide rule computer ca 1960, and SAAMI decreed CUP in 1969, which yardstick does the Powley Computer use? Is it the SAAMI CUP yardstick, or the CIP/military "psi-copper" yardstick?

KenO

Sorry Paul5388, I'm not sure what your point is. The Pressure Computer is fairly insensitive to charge weight, so the density doesn't matter. Using the numbers I have for the 6 Rem (55 gn case), I get the Load Computer predicting a charge weight of around 47 gn to the case mouth. All of the powders you cite will fit in the case at that charge weight.

The Powley Load computer does not try to predict max loads. It tries to predict a somewhat reduced load (40,000 to 50,000 as indicated by crushers) which will nearly fill the case below the bullet. For 100 gn spitzers, I get it estimating 43 gn 4831 to be suitable, and for 80 gn spitzers, 45 gn 4350. In both instances, these are below max in IMR's data -- just what Powley intended.

This is off topic, Paul, but I'd be happy to continue this via PM.

KenO, after your descriptions of the old crusher methods, the same thoughts occured to me, and yesterday I re-worded some passages in my implementation of the Powley Computers to state that the use of "CUP" there is not correct. The instruction booklet refers to pressures as "psi" but I can't believe electronic measurement was that common for published sporting loads at that time; I've always assumed it was crusher.

On the other hand, Powley may have worked from DuPont's data, which was pretty extensive even when Phil Sharpe did his big book years before. If I had Sharpe's book on hand, I'd go look up his description of the then current crusher methods. It might hint at whether DuPont drilled the cases for its tests.

If I understand your description of the problem with the CUP style crusher tests, not drilling the case can cause extra undershoot or overshoot compared to drilling. Perhaps it would average out over many different cases and loads? If so, Powley's curve fit would not be affected. Lastly, the general agreement between CIP crusher and SAAMI CUP ratings might suggest that these two organizations weren't too concerned with the differences in the crusher methods. I wonder what method SAAMI was using in the '40s and '50s?

edit: I just looked at Davis's comments again. He says the term "psi (copper)" was common in "commercial" practice before the term CUP was invented. In military and foreign data, "psi" was used by itself.

I can only guess, but I'm inclined to think that Homer was familiar enough with the military thinking to see its weaknesses as well as its strengths and at the same time duly respect (and highly regard) the SAAMI thinking. He did, after all, work as employee and consultant in both realms. I know also (a) that he appreciated the value of the predrilled case under the crusher piston and (b) that he used the DuPont data extensively in the foundations of his studies and conclusions.

Much of this will become clearer, I'm sure, when I'm finally able to get Homer's books and all his technical memos into print. Partial collections and fragments of his memos are scattered more widely abroad than the early Christians in Acts, but I have the only extant collection of all his technical memos. Someday � [sigh]

Seems to me that under ideal, controlled circumstances the thing that is being measured does not change appreciably regardless of the method that is being used to measure it. In other words, the differences in measurement are the result of problems with the method of measurement rather than the thing that is being measured.

Eliminate the problems with the methods of measurement and there should be a correlation between the measurements produced using different methods.

That's absolutely true, CH. Except that there is no system or method that eliminates all the problems. Every method employed in the past and present has unfortunately had a different set of problems to cope with. If you pardon an "algebraic" analogy, we can't get a true "equals" formula because the problems on either side of the equation never quite cancel out.

Pummeling a deceased nag won't ever bring it back to life. Not even cats (contrary to the old wives' tale) have more than one life � and even some of those are born dead.

When developing handloads to be tuned for an individual strong rifle, pressure is but one phenomena related to the real concern in finding a max load: brass life.

"Much of this will become clearer, I'm sure, when I'm finally able to get Homer's books and all his technical memos into print. Partial collections and fragments of his memos are scattered more widely abroad than the early Christians in Acts, but I have the only extant collection of all his technical memos. Someday � [sigh]"

I hope you do find the means to put them into some form of publication. I don't have the scientific acumen to make much of them, I'm sure, but that doesn't mean I wouldn't value a chance to peruse them.

From time to time we get a hint at volumes of information or research that has been lost to us because it existed in only one location and someone did not see the value in it - Hervey Donaldson's files for instance (if I even got the name right).

I hope you have trusted friends who will preserve Powley's writings if you don't get them published. And I don't mean this as if I know you or know how to properly value Powley's materials. I mean it to apply to anyone who has accumulated historical documentation of this sort, relevant to our fascination with firearms and shooting: Please keep your materials safely stored, properly identified and properly conveyed to an appropriate trustee via your will or other arrangements.

Sorry for bring this up late.I have been away..Why does the 444 Marlin have a SAAMI of 44,000 CUP and 42,000 PSI?It was built as a rifle cartridge not a pistol cartridge..The math on Denton's formula makes it 48,000 PSI with change..

Just never understood CUP being higher at this pressure than CUP.

Jayco