I'm sure this has come up before but I guess I missed it, or didn't care at the time but....

In another thread a question is asked about load data. While looking up some I noticed that on IMR's web page they have both PSI and CUP listings for different bullet weights. For instance one weight bullet with different powders rated at PSI and the next heavier bullet listed with each powder rated in CUP.

How close are the two? Where do I look up the SAAMI ratings for each cartridge inPSI and CUP? Nate

They are not close, there is no simple direct conversion method, and some of the older data that is actually in CUP gets shown as PSI. (CUP and PSI were used interchangably prior to electronic pressure measurement) It's a big mess.

Fortunately, it does not matter much since the average hobbyist has no way of measuring pressure nohow.

You can buy the SAAMI manuals from SAAMI, but I believe each cartridge is spec'ed in CUP or in PSI - not both.

Try Steves` web site for comparisons. http://stevespages.com/crusher.html

CUP is obsolete but still permitted by SAAMI. Powder companies seem to be buying PSI pressure barrels for new cartridges but still use CUP barrels for old cartridges. I guess the pressure barrels are pretty expensive so they are reluctant to upgrade.

There is a empirical conversion formula for bottleneck cartridges that correlates fairly well. You can find it as a tech article on the RSI website. Sorry, I don't have it at my fingertips.

But mostly it is better to use PSI data whenever possible and not worry about CUP.

quote:

There is a empirical conversion formula for bottleneck cartridges that correlates fairly well.

Here is one.
http://www.shootingsoftware.com/ftp/psicuparticle2.pdf

.

quote:

Originally posted by popenmann:
...There is a empirical conversion formula for bottleneck cartridges that correlates fairly well. You can find it as a tech article on the RSI website. ....

I may be wrong, but I'd bet this "RSI Tech Tip" is more of "denton's ignorance" still duping folks.

According to "El D", even Dr. Oehler has written a recent Article and said(words to the effect) that any correlation between CUP and PSI is full of beans.

.

quote:

Originally posted by Hot Core:
even Dr. Oehler has written a recent Article and said(words to the effect) that any correlation between CUP and PSI is full of beans.

Oh, BULL. Dr. Oehler wrote the article more than 10 years ago, and established a near-perfect, nonlinear conversion between the two.

And no-one cared.

The reality is that CUP is about as obsolete as dram-equivalents, and should be allowed to die a silent, merciful death. FWIW, Dutch.

quote:

Originally posted by ALF:
How can there be a correlation?

Think logically about it !

I've said it before and I'll say it again. If 2 measurement systems measure the same thing, AND IF THEY ARE BOTH GOOD, ACCURATE SYSTEMS, they are forced to correlate. A=C and B=C, therefore A=B. Yes I know CUP is skewed by the continued deformation during other than peak pressure times of the firing event.

HotCore may not like Denton, but his empirical analysis of the data speaks for itself. Until someone shows me his error directly, I'll continue to believe his data. He showed a pretty clear correlation. Note that CORRELATION and CONVERSION are 2 different things...

.

Hey Alf, those graphs look real similar to graphs from the same sources that you have mentioned L.E. Brownell, DuPont, and UM. They came from a ?1966 article in the 3rd anniversary edition of Handloader's Digest. The article, called-Ballistic Breakthrough-about the then new strain gauges, talks not only about the problems and limitations of the crusher system mostly but also the piezo system(not useful above ~70K psi).

From memory, one of Denton's formula
ANSI PSI = 17902 + 1.51586 x ANSI CUP

Absolute linear conversion? No Way. Trust for a max load conversion? Not a chance. Is there a correlation between the systems? Without doubt.best-o-luck

quote:

From memory, one of Denton's formula

If I trust my memory I thought you subtract the 17902

.

I just found my Sept issue of Shooting Times and Mr. Oehler (I think it was) had an article on this very subject.
I read it but basically it sounded to me like there was more evidence that CUP was non-linear and psi was a better measure of actual peak pressures.

My main concern is that in the same book, under a single cartridge were readings in psi for one weight bullet, and the next weight of bullet was in cup. If the limits for cup and psi are not expressed then where is the limit? Nate

quote:

Originally posted by lonniemike:
...From memory, one of Denton's formula
ANSI PSI = 17902 + 1.51586 x ANSI CUP

Absolute linear conversion? No Way.

Trust for a max load conversion? Not a chance.

Is denton an idiot constantly mis-leading otherwise good folks? Without doubt.
---

Hey cdh, What do you think the two lines in the top chart that alf posted tells you about:

quote:

Originally posted by CDH:
A=C and B=C, therefore A=B.

Can't you see there is NO coorelation?

In order for your "A=C and B=C, therefore A=B." to be valid and worthwhile, it must apply across the "entire Range", and of course it falls flat on it's nose - in a Cow Flop - just like the rest of "denton's great discoveries".

Ramrod good eyes and memory. So much for my memory. You are correct it is a negative integer(-17902) instead of a positive integer(17902).

CORRECTION


ANSI PSI = -17902 + 1.51586 ANSI CUP (or so)

PSI (strain gage) data cannot be correlated to CUP by any SINGLE correlation mathematical relationship. The reason is that the output of the CUP measurement cannot be describe by a single exponential expression ie it is not a continous function!

Denton's equation does not come remotely close to correlating to either of the plots provided by Alf.

One can get some correlationships within narrow bandwidths (say 5000 to maybe 10000 psi), but you will not find a single relationship to describe a correlationship between PSI and CUP that covers anywhere near the full range of center fire smokeless rifle loads (25000 psi through 65000 psi).

Sorry to burst any bubbles.

quote:

Originally posted by Hot Core:

Hey cdh, What do you think the two lines in the top chart that alf posted tells you about:

quote:

Originally posted by CDH:
A=C and B=C, therefore A=B.

Can't you see there is NO coorelation?

In order for your "A=C and B=C, therefore A=B." to be valid and worthwhile, it must apply across the "entire Range", and of course it falls flat on it's nose - in a Cow Flop - just like the rest of "denton's great discoveries".

Without knowing what they are calling a 'correlation factor' the top graph doesn't tell me much. It certainly looks like a graph of CUP vs. PSI, but isn't labelled as such. Even still, the general trend is there, especially if you lop off the totally unnecessary ranges above 65kPSI as they are beyond the range of small arms under discussion. Yes it diverges steadily as pressures rise, but this graph CAN be modelled if one so desired. Same number, no. Outside the limits of high school mathematics? No. See graph #2 (figure 14).

The bottom graph says very clearly "Approximate Relation Between Absolute Pressure (assumed to be peak pressure) and Crusher Values". That speaks pretty strongly of a relationship. It's a curve on a log-log scaled graph paper, BTW, since you seem to be unable to read it. A single curve. That's called a function in mathematics...making it eminently identifiable by a SINGLE mathematical equation.

Yes, I see that it's also labelled approximate. I never claimed they were directly convertable, just that they correlate. Without knowing the data Alf's graph is generated upon, we can't judge how 'approximate' the 'Relation' is, but it's there, plain and simple.

But nothing is simple with HC involved...is it?

quote:

Originally posted by CDH:
...But nothing is simple with HC involved...is it?

As long as people end up providing incorrect information for the Rookies, I'll try my best to point out where they are TOTALLY MISLEADING everytime I see one of those posts.

As can be seen by everyone, when push comes to shove, then "you" are forced to admit that, "A=C and B=C, therefore A=B." is not ALWAYS 100% accurate, "...it's also labelled approximate. I never claimed they were directly convertable, just that they correlate."

Apparently you really don't have any idea at all how that can mislead the Beginners or Rookies who are trying to make some sense of these posts. They will take something like the "A=B" thought and extrapolate an incorrect result.

I in no way think you do it intentionally. Perhaps you just haven't considered who comprisies the entire viewing audience.

Where in denton's case, he never could understand the concept that misleading Beginners is a bad idea, I do believe you can and will understand.
---

By the way, I see one additional correction that you really need to make. It would be an "addition" to your Tag Line:

quote:

Believe nothing, no matter where you read it, or who said it, unless it agrees with your own reason and your own common sense.

You really should add, ...unless Hot Core says it and then you can count on it being 100% factual and True - all the time!

quote:

Originally posted by Hot Core:
is not ALWAYS 100% accurate,

Nothing is ever totally 100% accurate. Nothing. Not even you.

Where I get annoyed is with your constant higher than thou attitude. I have a wife, and there are plenty of nannys in the world. Leave the 'protect the masses at all costs' nagging and nannying to the democrats. Sometimes you gotta take some personal responsibility, and if one is at this point to worry about such details as we are discussing, they damn well should be able to make and live by the call in my sig by themselves.

Call 'em like you see 'em, but leave the asshole behind, lest the message be lost in the heat of the language.

Would it really matter or help if instead of A=B I said:

MAXPSI FOR RECIPE A=60000PSI (C=A)
MAXCUP FOR RECIPE A=52000CUP (C=B)
THEREFORE 60000PSI=52000CUP FOR RECIPE A (A=B)

If someone gets the idea through looking at data that since recipe A shows 52000CUP here, I can really juice the loads up to 60000 cause they believe the numbers are interchangable, well, I just don't see that as a logical conclusion from any discussion here and I don't see how their stupidity in not following the golden rules of reloading, such as 'work up, and 'max is max' can be laid at my feet...

Enough pissing for one day.

Now Hot Core, clearly CDH -- and denton as well -- is correct: CUP and psi are correlated. Higher pressure cartridges generally have higher CUP and higher psi ratings. Further, if you increase the charge in a given cartridge, both the CUP and psi readings increase as well.

Thus there is some correlation. Whether the correlation is good enough to be useful, that is debatable, of course. On that issue, I think the fact that firearms designers produced sound guns for decades measuring pressure only with crushers is proof enough that crushers are practical.

Denton's "curve fit" was a simple linear one, fitted to data only above 28,000. It clearly doesn't go through one obvious data point -- 0 CUP is 0 psi -- and that is a typical shortcoming of a plain-Jane least squares curve fit.

SAAMI rates many different cartridges in both CUP and psi. All of the older cartridges are rated in crusher readings, and to establish a modern psi limit would surely require firing a wide variety of charges and bullet weights to establish what a typical true pressure is. It is for this reason, I believe, that SAAMI doesn't have a psi spec. for all the oldsters; it's too much trouble for the limited demand.

Denton has also clearly demonstrated that the CIP does use a simple, linear conversion formula, and the CIP sets the proof standards for most of the world, which indicates such conversions are not useless.

One thing to note from the curves ALF posted is that CUP's underestimation of pressure (in that cartridge) gets ever worse as the pressure rises. One curious side effect is that rifles proofed in CUP are actually proofed to a higher standard than those proofed in psi.

quote:

Originally posted by CDH:
...Where I get annoyed is with your constant higher than thou attitude. I have a wife, and there are plenty of nannys in the world. Leave the 'protect the masses at all costs' nagging and nannying to the democrats. Sometimes you gotta take some personal responsibility, and if one is at this point to worry about such details as we are discussing, they damn well should be able to make and live by the call in my sig by themselves.

Hey cdh, Nope, I still intend to point out how the Beginners and Rookies can be mis-lead by posts that simply are not 100% true. Doesn't matter to me who posts the misleading ignorance.

I remember when stanly got his M43 and was posting on Shooters many, many years ago about his "Loads". I was as interested as anyone and looked forward to seeing what he had Tested.

One day he was posting Loads for a 30-06 that looked like a lot of Powder and very high Velocities to me. I asked if it was a typo and stanley came back to say the loads were SAFE in his rifle, but they were close to 100,000psi(M43).

Then I asked if everyone didn't think that could possibly be misleading to the Beginners. Got some interesting responses, many of which were similar to "your" thoughts that the Rookies should know better. Of course that prompted some heated exchanges and the words you use which imply that "everyone should look-out for themselves" were similar to what stanley used.

The problem with that entire line of thought(from my perspective) is the Beginners don't know enough to always understand how something as you posted(and ALL of denton's total ignorance) can get them into Pressure Problems.

Either you don't understand how Beginners can be mislead, or you don't care if they are. Doesn't matter to me, cause whenever I see posts that can be misleading to the Rookies on this Board, I intend to dive right in and let the chips fall where they may.

quote:

Call 'em like you see 'em, but leave the asshole behind, lest the message be lost in the heat of the language....

You may be a Preacher where you come from and you may be able to tell other folks how and what they should post and think, but you only make a complete fool of yourself when you believe you are in my Chain-of-Command.

Your "directives and preaching" in an attempt to divert the subject from your misleading, potentially unsafe posts, simply don't impress me.

There does seem to be an abundance of Preachers on this Board who actually think they can tell other people how they should post. I much prefer to discuss things in a civil manner, even when I disagree, but intend to give it back in the same tone I receive.
---

Just to show everyone I can get along with the entire thought process that cdh is trying to make, I'll agree there is EXACTLY "one Pressure Point" where CUP=PSI=CIP=Transducer=X, on every cartridge in existance.

For one additional "hint", denton's ignorance even gets that one Pressure Point TOTALLY Wrong.

So, now cdh is not 100% Totally misleading, but denton's ignorance is still all WRONG.
---

Hey asdf, I see you are beginning to fill in some of the disclaimers necessary to make the above misleading ignorance - somewhat more relevant. That is not intended as faint praise, if all the "limits and disclaimers" were included with denton's ignorance, then it would be quite different. Of course that would then limit the "range" of it usefulness to such a small area as to then be totally worthless.

But as you can see in lonniemike's post:

quote:

From memory, one of Denton's formula
ANSI PSI = 17902 + 1.51586 x ANSI CUP

none of the limits or disclaimers are included.

By the way lonniemike, it really doesn't matter if the 17902 number is positive or negative, the whole concept is WRONG.

quote:

There does seem to be an abundance of Preachers on this Board who actually think they can tell other people how they should post.

...and the king of that list is quoted above.

Which do you prefer to be called, pot or kettle, because you are the queen of it on this board.

quote:

You may be a Preacher where you come from and you may be able to tell other folks how and what they should post and think, but you only make a complete fool of yourself when you believe you are in my Chain-of-Command.

Ditto and right back at 'ya! Actually I wasn't trying to be preachy...just offering some advice that the MANNER in which something is stated can often times override otherwise worthwile information. You come across as an arrogant jackass to many...I've seen you called that and worse by others in the few years I've been here on AR...and if you fail to see how that can completely destroy any semblance of credability you may otherwise posess, well, you know the old saying about leading horses to water, don't ya!?!?

If I came across as preachy, well, that's my problem when I'm biting my tongue trying to keep from acting like your old drill instructor. Your 'my way or the highway' attitude would make you a fine democrat. Have you considered becoming a politician??? We live in an over-lawyered over-sensitive overly PC world where attitudes like yours grate me every day.

quote:

Either you don't understand how Beginners can be mislead, or you don't care if they are. Doesn't matter to me, cause whenever I see posts that can be misleading to the Rookies on this Board, I intend to dive right in and let the chips fall where they may.

You are gonna stay busy I guess. Every time someone posts a favorite load (usually several grains over published max) followed by the 'disclaimer' "It shows no pressure signs in my rifle" you should be all over them. That's probably about a dozen times a day...

Just for HC and any rookie/less experienced reloaders reading this: The previous information is for advanced reloaders and academic use only. If you don't understand this fully, you shouldn't be making use of any information being disseminated in this thread.

quote:

Just to show everyone I can get along with the entire thought process that cdh is trying to make, I'll agree there is EXACTLY "one Pressure Point" where CUP=PSI=CIP=Transducer=X, on every cartridge in existance.

...and when you plot such relationships (above zero, I know that was the point you are referring to ) as PSI to CUP you get the second graph Alf posted above. A graph that is eminently suited to being modelled by a mathematical equation. The question of whether it is suitable for predicting loads is valid at this time? Probably about as suitable as using any other software predictor like Quickload...it'll get you into the ball park but it requires a much greater level of caution than simple adherence to published data.

Such is the fun of reloading...all standard disclaimers apply.

CDH,

quote:

the second graph Alf posted above. A graph that is eminently suited to being modelled by a mathematical equation.

Would you be so kind as to post that single mathematical equation?

Thanks

Scott, unfortunately using the graph alone to generate the function is fraught with difficulty (accuracy in reading the data points to a reasonable precision) and backwards. The raw data should be used to generate the equation and the graph.

I do not have the raw data.
I do not have the patience to withstand the kind of attacks some on this board seem to relish, were I to actually publish it.

High end regression techniques may be required, and that's the realm of programmers, mathmaticians, and statisticians...not engineers like myself.

HC will howl, but you can decide for yourself...Denton did something remarkably similar by using the SAMMI CUP and PSI maximum values for raw data to generate the equation mentioned above. Look at the second article on the page I linked below:
Good reads

To data any reasoned, technical debunking of these articles is conspiciously ABSENT from all discussions therein. Denton himself allows in that article that it's good to (IIRC) 3000PSI. Far from perfect, but given the shot 2 shot variation inherent in most factory loaded ammo, it's at minimum a useful additional piece of information. 1500PSI high or low is NOT going to put any sane reloads over the edge.

As much as I love getting deep into the technical aspects of our hobby, the raw emotion that seems to flow when actually trying to hold a reasonable discussion pretty much ruins it.

I think that CUP and PSI is more usefull in providing us something to talk about than any profound value in saving our rifles. If you don't have the equipment to measure either, you wii never know what your gitting. To much difference in chambers and barrels. also bullet seating depth will change pressures.

The most reliable pressure indicators are the one's you find by studing your fired cases. But whatever your cases tell you, you still won't know what chamber pressure was! Weather PSI or CUP

quote:

The most reliable pressure indicators are the one's you find by studing your fired cases.

Unless you have on old Ballard, where the breech might break before the brass does...

ScottS, you can find one such fit to that data here, about 2/3 the way down the file.

Yes Hot Core, I fully agree there are MANY caveats to CUP and psi conversion. Denton does mention the likely accuracy of his conversion, based on statistical methods. A problem with that is that his curve fit is based on SAAMI limits for those cartridges spec'd in both CUP and psi. SAAMI probably sets a fairly conservative psi rating when "updating" the pressure spec from CUP to psi. Still, I seriously doubt that all loads meeting the CUP spec also meet the psi spec as well. The error CUP has from true psi probably varies with powder, relative case size, bullet construction, etc. And yes, it is annoying to see 5 significant digits in a conversion formula where even 2 digits is optimistic. And I do wish Denton had taken the time to run his analysis with the formula anchored at The Common Point -- but the CIP didn't bother to go through It either.

Still, given the factor of safety which must be designed into a gun, I do not feel that the conversion errors are so great as to dismiss the conversions entirely.

quote:

Originally posted by CDH:
...above zero, I know that was the point you are referring to ) ...

Hey CDH, I should not have provoked you in my earlier posts. DO NOT view that as any kind of appology, because I don't believe in appologies.

That said, it was obvious to me from this thread and a couple of others that for whatever the reason, it would "wind you up" for me to needle you a bit. Really shouldn't have added additional stress to whatever the burden is you are currently dealing with.
---

Anyway, CDH got it 100% correct in his above statement that "denton's formula will work - properly - at ZERO Pressure". (Of course that is the ONLY place it works.)

No need for me to say more since all the disclaimers are now beginning to appear throughout the thread in both CDH's and asdf's posts.
---

Maybe denton could share some of his Mylanta with you. Rumor has it he used to get the 55gal size when he "tried" to hang-out here.

quote:

Originally posted by asdf:
Denton does mention the likely accuracy of his conversion, based on statistical methods. A problem with that is that his curve fit is based on SAAMI limits for those cartridges spec'd in both CUP and psi.

***

Still, given the factor of safety which must be designed into a gun, I do not feel that the conversion errors are so great as to dismiss the conversions entirely.

Ka-ching! My how easy it is to discuss things in a technical sense if one looks, and doesn't get all emotional about it. 30 minutes today during lunch and I replicated Denton's experiment. Try it. There are additional holes...but none of them change the basic facts we are debating.

For example, his not anchoring the data at 0PSI=0CUP could be a flaw, and it could be good because CUP doesn't register at low pressures where brass wouldn't deform. Debatable, heck yes. Fatal flaw, I don't think so.

For example, he uses linear regression and gets a .927 correlation factor. Good, but use a lograthmic regression and you get a .939 factor. Even better, the factor detoriates a lot less with a true zero crossing with a logramithic regression.

For example, the assumption that SAMMI CUP and PSI are the same pressure, i.e. a true reading of the same event with CUP and PSI instruments will result in the SAMMI values, is debatable. A fatal flaw, probably not, but debatable, heck yes.

For example, the assumption that CIP uses a mathmatical model to generate their data simply because it's so tightly correlated is debatable. They may simply measure both at the same time, or have better controls. Debatable, heck yes! Fatal flaw, no.

Spreadsheets are wonderful tools...and asdf makes a very good statement at the end of his post...

quote:

Originally posted by Hot Core:
[
That said, it was obvious to me from this thread and a couple of others that for whatever the reason, it would "wind you up" for me to needle you a bit. Really shouldn't have added additional stress to whatever the burden is you are currently dealing with.

Now you're a psychologist. Nice. My only burden is dealing with excessive stubborness and thinking that a reasoned, mentally stimulating debate could come of all this...

quote:

For example, the assumption that CIP uses a mathmatical model to generate their data simply because it's so tightly correlated is debatable. They may simply measure both at the same time, or have better controls. Debatable, heck yes! Fatal flaw, no.

If so, not a fatal flaw at all, in my view. Denton's plot of the CIP data is so flat -- basically only round off error -- I don't see how it could be anything but a linear CIP-to-psi conversion formula. For it to be otherwise, then CUP is remarkably linear over a wide range of pressures and over a wide variety of relative cartridge dimensions. Given the spreads in the SAAMI data, I doubt this is possible. But, anything is debatable.

asdf,

Thanks. The Brownell equation isn't entered correctly in the link you provided however. You will discover this very quickly if you attempt to convert CUP to PSI using it. None of those conversion equations is very accurate, by the way. Some are fit well within narrow bandwidths. This is easily seen graphically by simply plotting the true CUP vs PSI plot that Alf provided and each of the three conversion formula outputs (Denton's, CIP, and Brownell).

I fear there is no single convertion between CUP and PSI.

Plot of Alf's PSI vs CUP curve and the three conversion equations (Denton's, CIP, and Brownell)



Neither Denton's (worse fit) or CIP (very close 2nd worse fit) fit the curve at all! The Brownell conversion is damned good up to ~ 50,000 psi and then accuracy goes to crap (right where the majority of modern smokeless centerfire rifle cartridges operate).

You guys must be bored if all you have to do is argue about an obsolete measurement system.

Denton got his data points directly from SAAMI. His curve provides a good fit for those SAAMI numbers -- for rifles only, since Denton didn't include pistol data. Whether the SAAMI numbers are accurate are another story, since SAAMI doesn't tell us how they come up with their specs.

Case in point: 357 Magnum
SAAMI psi = 35,000 psi
SAAMI CUP = 43,000 ??? (not sure but Hodgdon goes to about 43,000 CUP)

According to the Brownell curve that Alf posted, 43,000 CUP = 48,000 psi, or thereabouts. This disagrees with the SAAMI spec. Either the SAAMI spec is wrong, or else the Brownell curve is wrong.

Whether the relationship is linear isn't important. It is entirely feasible to create mathematical models for non-linear relationships. People do it all the time, and Denton knows that. However, his linear curve produced a good correlation over a narrow range (remember, he was only looking at rifle cartridges -- his curve does not cover pistol cartridges).

I say again the best approach is to use PSI data whenever possible and ignore CUP. Unfortunately, there is a shortage of PSI data for some cartridges like the 357 Mag.

ScottS, sorry about that. The equation I give there is not based entirely on Brownell's data. I wanted it to have the shape of Brownell's data, but I tried to tie it closely to some typical SAAMI ratings, where 52 kCUP is usually near 63 ksi. I didn't worry greatly if accuracy fell off in the proof pressure range. It's a pretty good fit from 0 to 52 kCUP, and that's all I worried about since I'm not aware of cartridge rated at over 54 kCUP.

I believe Brownell's data is based only on .30-06 firings. I doubt his data is representative for all rifle cartridges.

popenmann, it's hardly obsolete. Many useful production cartridges have only crusher ratings. It is obsolete for new designs, but it is neither obsolete nor useless.

The conversion formulas are NOT EXACT. As far as I can tell, there is NO accurate conversion. The error in CUP is, I believe, a function of many variables. It is not just a function of true pressure.

As for the .357, I have noticed that one. BTW, it's 45 kCUP for the .357. I've also noticed over the years, that .357 data developed in CUP has higher fps ratings than those developed in psi. Indeed, it's hard to find psi data for the .357 any more. I think SAAAMI, for whatever reason, underrated the .357 when it developed the later psi rating.

/

ALF: I'm curious about your thoughts for the reason CUP is low. I had thought of the friction reason, but piezo sensors also use a conformal piston. Perhaps the case being blanked into the piston bore has some effect. Perhaps the crushers tend to deform a bit crooked, causing the piston to bind some.

You mention strain rate, but I'm not familiar with that concept. If by this you mean there is inertia in a crusher and its piston, I agree, and I suspect that is the reason CUP is low. I imagine the pressure spike is brief enough that the crusher didn't finish crushing before the pressure began to drop.

I don't see your argument about plastic deformation. The deformation is calibrated in static tests. If the pressure rise rate is slow enough, the crusher will correctly measure pressure every time. It has to. That's how the crushers are calibrated. In a gun firing, the pressure rises MUCH faster than in the calibration tests, and, again, that's what I see as the rub. I plan to run this throught a finite element analysis in a few months, just for grins. Yeah, I like old technology.

edit: ok, I found some information on "strain rate". The Wikipedia mentions "the stress at which yield occurs is dependent on ... the rate of deformation (strain rate)" and in the documentation for the LS-DYNA finite elements software is mentioned it can take this into account; interesting, and obviously a factor here.

popenmann: I remembered RamShot only develops loads in psi. They keep their loads to SAAMI's 35 ksi, and in a 10" barrel can get no better than 1400 fps with 158 gn bullets using their dense, ball powders. Hogdon develops their loads in the same length barrel but with CUP and they can get over 1500 fps with stick powders and 1600 with ball while staying within the SAAMI CUP limits. I truly believe the SAAMI CUP rating is at a higher true pressure than the SAAMI psi rating. I can think of a couple of reasons why they would choose to do this, but I'll spare our readers my ramblings (for this time).

asdf,
Sounds like you are an intelligent person. Thanks for contributing to the discussion. We need more intelligent people on this forum.

Regarding the Hodgdon 357 data, IT IS WRONG AND SHOULD NOT BE USED. Wrong pressures, wrong velocities. For example, they show more velocity out of pistol than out of a rifle with the same load -- WRONG !!! Also, their Lil Gun data is way off the map and should not be taken seriously. I have published some 357 strain gage data on my web site www.mountainmolds.com. The Hodgdon 357 CUP data is a perfect example of why the CUP system is obsolete and should no longer be used.

To all, wikipedia has an excellent discussion of the CUP issue and lo and behold, it lists the Denton article as a reference. Gee, I wonder why they didn't list Hot Core as a reference?