PSA Vs CUP

[No_1]

My Mistake on the title. It should read PSI Vs. CUP

I found this on the web and it kind of makes sense. Please review and give your comments.

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

[felix]

Math wise, it's OK, Robert. But the most significant thing missing is the fact the measurement transducers are not alike. Because they are actually used for the same purpose, the confusion arises. The transient response of the devices has to be taken into account, and there has been no mention of that anywhere. In other words, the differential equations representing/approximating the immediate/realtime pressure trace are completely devoid in the discussion. So, because the copper crusher method is so slow (crushing/non-linear) in reporting "max" pressure as compared to the piezo crystal (squeezing/linear), the more accurate measurement is for the piezo.
Moral of the story: use data from each measurement independently, and do not cross contemplate the values. In summary, always think one, and not the other.

What we need from the labs are piezo measurements every inch down the chamber-barrel from the rear of the case to the muzzle. To keep the reporting simple, we would require the summation value under the curve, and a measurement of sorts of how the tails shift towards the rear (case rear), and towards the muzzle.

... felix

[BD]

To me this article largely disproves it's own theory. If I'm getting this correct, he starts with only 32 chamberings and then arbitrarily discards 25% because they don't fit his theory. Then the graph of the remaining results has a few points nearly 10,000 psi off the corellation. To me 10,000 psi is way to much latitude in estimating pressure for reloading. I feel that a much more accurate premise would have been that "CUP and PSI can be correlated closely in SOME cartridges, but do not correlate well in others."
How many cartridges are there anyway? 32 does not seem like that many to start with.
BD

[BD]

This article has been sort of rumbling around in the empty space in the back of my head this afternoon and another aspect of his theory occurred to me. He is correlating Saami max pressure points and claiming that as evidence for a strong correlation between PSI readings and Cup. To my thinking for a study like this to prove a level of correlation useful to reloaders one would need to compare actual pressure readings from several specific load workups in any particuler cartridge. All this article has really shown us is that a specific pressure level can be expressed in both Cup and PSI. I think we already knew that. For his premise to be valid his formula would have to be accurate across the spectrum of pressure readings throughout a load work up, plus or minus a margin of error within our "comfort margin".
BD

[monadnock#5]

I remember reading many, many moons ago, that the CUP measurement system was designed specifically to preclude interpolation of data by reloaders. The powder companies started out using PSI as the pressure standard, but found that there were individuals with technical backgrounds who read the reloading manuals, did the math, and came up with their own reloading data. These individuals did a good job of destroying firearms and hurting themselves. It was then that the engineers came up with a system of measurement that no one outside the industry had access to.

I'd like to hear what the Lyman or IMR engineers have to say about the treatise you've posted a link to. But I think I already know.

[No_1]

I must agree with you completely. Those were the thoughts I had that made some of it make sense. But just like you I figured there needed more testing. I wanted to post this as food for thought since there has been post about this before.

R.


This article has been sort of rumbling around in the empty space in the back of my head this afternoon and another aspect of his theory occurred to me. He is correlating Saami max pressure points and claiming that as evidence for a strong correlation between PSI readings and Cup. To my thinking for a study like this to prove a level of correlation useful to reloaders one would need to compare actual pressure readings from several specific load workups in any particuler cartridge. All this article has really shown us is that a specific pressure level can be expressed in both Cup and PSI. I think we already knew that. For his premise to be valid his formula would have to be accurate across the spectrum of pressure readings throughout a load work up, plus or minus a margin of error within our "comfort margin".
BD