Hey dutch, I can't help it that Dr. Oehler AGREED with me concerning the Haphazard Strain Gauges, or that he agreed that no rational person believes a conversion from PSI to CUP exists. I do understand your frustration in that Dr. Oehler's words - blew you and denton completely out of the water AGAIN! Or perhaps it should be "as usual". Big Grin

I gleaned the above from another reloading thread post. I have included all but the relevant part is in red.

I have also read to not believe any conversion formula on the internet that says "X" lead units of pressure (LUP), or "X" copper units of pressure (CUP) equal "X" pounds per square inch (PSI). However, I did just come across this statement in a 1985 Winchester reloading components catalog:

"Pressures are designated by "CUPS" and "LUPS", meaning 'copper units of pressure' and lead units of pressure.' The actual numbers are identical with those designated in the past as P.S.I. (pounds per square inch)."

This might be a good lesson to not take info found in old reloading books as gospel.

quote:

"Pressures are designated by "CUPS" and "LUPS", meaning 'copper units of pressure' and lead units of pressure.' The actual numbers are identical with those designated in the past as P.S.I. (pounds per square inch)."

I believe this is because all during the early and middle years of the 20th Centruy the US ammunition industry had no means of measuring pressures other than the crusher method, but were referring to their results as "PSI" rather than the later terms of "CUP" and "LUP" despite the fact that these figures were actually NOT PSI.

I would suspect it went something like this in the early years...vastly simplified but you should get the point.

A) We have a copper pellet, crushed x" in the CUP method
B) A hydraulic ram required y PSI to duplicate x" of deformation
C) therefore x" CUP=y PSI

This totally ignored the transient nature of the CUP/LUP deformation and when 'accurate' PSI measurements because available this skew became apparent.

We have totally beaten the CUP to PSI issue to death in other threads...

I believe it was denton that extrapolated an equivalancy for PSI to CUP.....as I recall he further stated it was only close for a certain range and that the data was for reference only.

I still use that as reference for purposes of estimating if a particular round can be "improved upon" when it's listed in manuals as "CUP" It has proven useful to me and I still use it at times.

Like all things.......it needs to be put into context before it becomes useful.

onefunzr2, Winchester's statement from 1985 is 100% correct.

For a long time, the industry labeled as "psi" what today we label "CUP." This was technically correct, for CUP is indeed a psi measurement. However, copper crushers accurately record peak psi only when the pressure rises and falls relatively slowly. In a rifle, the pressure rises and falls faster than a crusher system can track. Crushers generally indicate a peak that is below the actual peak pressure.

While the crusher reading indicates in psi, it is has long been known (since the 1800s) to be an inaccurate measurement of peak psi. For this reason, the industry starting using the name "CUP" for peak psi measurements made with crushers. This clued the reader that the measurement was not as accurate as those done with more modern techniques. This distinction only became important as labs began to switch to piezo systems, which can readily track the brief firing pressures in a gun. In some documents, pressures are reported as "psi-copper" and "psi-piezo" to distinguish them.

The errors intruduced by CUP are not terribly important, so long as the gun is proofed with CUP measurements as well. Indeed, there is reason to believe that guns proofed under the CUP standard are actually proofed to a higher relative pressure than those proofed with piezo measurements.

There are dramatic differences in the pressure measurements recorded with copper crushers depending on the test protocol used. CIP and the US government usually used the "drilled case" method while SAAMI used the "undrilled case" method. Before I make any use whatsoever of a copper measurement, I feel that I must know the test protocol used. Results from SAAMI or government tests can usually be assumed to have the appropriate pedigree. All other references to CUP or "psi-copper" are questionable unless the test protocol is explicitly documented.

KenO

KenOehler has correctly pointed out that in my previous post, I was playing rather loose with the term "CUP." Correctly used, CUP not only tells you a copper crusher was used to make the (inaccurate) measurement of peak psi pressure, it also tells you what shape the crusher was, what size the piston was, where on the case body it was located, etc. These are all specified by SAAMI, and the term CUP is one coined by SAAMI to indicate crusher readings made to their standards. Change any of these variables, and you can get a different indicated psi reading from a crusher.

I should also have been more clear about what Winchester was saying. They were telling you that the method used to measure pressures in their tests had not changed; it remained a copper crusher. Before, the industry had been content to report the results using the units of the indicated pressure, namely "psi." Now, the results from these tests were to be labeled "CUP." KenOehler might know if 1985 was about the time that the term "CUP" was introduced. Also, when did SAAMI last change their standard for the arrangement of the copper crushers? When the term "CUP" was introduced, was there an accompanying change in the physical crusher system? If so, then Winchester's statement was not quite correct.

Maybe no rational person cares about measuring psi or cup in their own guns.

But Dr. Oehler has to make a living...

Well, I may not want to drill one of my guns to make a crusher measurement, but I do plan to try strain gauges one day. Because I don't try to get the last bit of fps out of a cartridge, measurement of pressure is pretty much academic for my needs; but for those who want top performance, a strain gauge seems to be the only way to go.

asdf,

I suspect that the "CUP" terminology was introduced by SAAMI in the 70's or 80's. Not being a member of SAAMI, I'm not privy to all their history or discussions. It came about as they started using the piezo transducers in about this time frame.

Neither do I know the history of when and why SAAMI departed from the older tradition of drilling cartridge cases prior to copper crusher tests. From a labor viewpoint, I can understand why they wanted to avoid drilling. I suspect that the decision was made long before piezo gauges were available and it is understandable that nobody comprehended the large differences between drilled and undrilled. Perhaps it was common commercial practice even before SAAMI was formed in 1926. I just don't know.

I've drilled a few of my own guns for pressure measurements, but I certainly don't advocate the practice. It's a lot of expense and trouble for the info you get. My philosophy is to follow the books and quit when I (1) get an acceptably accurate load, or (2) see any of the traditional pressure signs, or (3) reach factory velocity. I don't claim that any of my loads are miracles with high velocity and low pressure. I like to think that my loads are safe in my guns, but I don't claim that they are under factory maximum average pressure. I know better than to quote any sort of pressure number without having measured it. I've been fooled too often.

KenO

For the record, Hot Core is in error about my discussions with Denton and his calculations regarding CUP-PSI. Denton's calculations are correct, but in my judgement only apply to a limited number of cartridges, and at a limited pressure range. Those limitations leave the calculations to be interesting, but of little practical use. FWIW, Dutch.

quote:

Originally posted by Dutch:
For the record, Hot Core is in error about my discussions with Denton and his calculations regarding CUP-PSI.

Denton's calculations are correct, but in my judgement only apply to a limited number of cartridges, and at a limited pressure range. Those limitations leave the calculations to be interesting, but of little practical use. ...

Well, well, well..., I certainly DO NOT mind to be corrected when I see you putting distance between yourself and denton's loonacy. Glad to hear I WAS WRONG about your thoughts on this issue.

Nothing like the distance I put between you and I......

Dutch.

quote:

Originally posted by Dutch:
Nothing like the distance I put between you and I......

Dutch.

quote:

Denton's calculations are correct, but in my judgement only apply to a limited number of cartridges, and at a limited pressure range. Those limitations leave the calculations to be interesting, but of little practical use. FWIW, Dutch.

Agreed. His calculations can be criticized on several levels...none of which have ever been offered by our resident anti-Denton. I don't recall Denton ever professing they have far reaching applications either, but merely that they were an interesting and informative evaluation.

In truth, there is no reason to ever convert from CUP to PSI. The only use of listing a pressure in load books might be to inform someone with say a 45 Colt (or 8mm Mauser, or 45-70, etc.) that the load is a low pressure one for weak guns or a high pressure one for modern guns. Beyond these limited cases who cares what units were used for pressure measurement. Max load is max load. End of story. Exceed at your own peril.