CUP versus PSI????

J

JohnKSa

Administrator
I can't find anything useful relating pressure measurements in CUP to pressure measurements in PSI.

I realize that there is no formula or direct relation between these two different types of measurements and I understand the methods used to make the two different kinds of measurements.

But...

Does anyone have any rules of thumb that compare the two measurements. For example:

Will the PSI always be a larger or smaller number than the CUP number?

Are there reasonably reliable conversions that work in a single caliber?

Any help is appreciated!

John
 
L

Libertarian

New member
They're different units of measure. I'm sure that there is some formula to figure one yo the other but I don't think that CUP is used anymore as it is not all that telling in "real world" measures. I mean, so what if you know how many balls of copper a certain load will crush? I'd rather know the workijg and peak pressures generated as a better way of knowing how well a barrel or chamber will hold up. CUP is a hold over from the days before instant electronic records.
 
W

WESHOOT2

New member
ZERO NADA NO CORRELATION

Sorry, no math to correlate the two.
Best measure is PSI, but it MUST BE UNDERSTOOD that ALL ammunition-related characteristics are based on THE SPECIFIC gun tested.
The rest is just for comparing.........

(This is not a moot subject for me, but experience suggests that we're screwed.)
 
H

Hal

New member
Ditto the zip, zilch

CUP is to PSI as
partly sunny is to road conditions.

It only tells part of the story. CUP is still used in a lot of reloading data. I try to avoid loads where CUP is used. It tells the peak, but doesn't allow me to plot the curve of how the peak was reached.

(not a moot point for me either being a handloader.)
 
K

Keith J

New member
Right on....

Copper crusher measurements are not related to peak pressure since the former are a result of deformation of a copper cylinder by the action of the entire pressure curve. In other words, a longer pressure duration can produce a greater deformation of the crusher cylinder than an impulse of significantly higher pressure at shorter duration.

Copper crusher tests are significant as the material deformation is indicative of the weakest link in ammunition, specifically the case and primer's ability to resist the pressure and seal. This is a test with great repeatability for one specific cartridge. For instance, if a .30-'06 shows primer leakage and pocket growth with a certain load combination at x CUP, then another load that is approaching the same x CUP is nearing the maximum in the same case.

Piezotransducers and strain gage measurements map the entire pressure curve and provide great insight into the internal ballistics of ammo but should not be relied upon for a specific load maximum. For instance, a load that produces x PSI and doesn't leak/shuck primers shouldn't be used to make another load based on the peak pressure of x PSI for case failure could happen at lower pressures IF the pressure curve is flatter/longer.
 
K

Keith J

New member
Copper crusher measurements are not related to peak pressure since the former are a result of deformation of a copper cylinder by the action of the entire pressure curve. In other words, a longer pressure duration can produce a greater deformation of the crusher cylinder than an impulse of significantly higher pressure at shorter duration.

Copper crusher tests are significant as the material deformation is indicative of the weakest link in ammunition, specifically the case and primer's ability to resist the pressure and seal. This is a test with great repeatability for one specific cartridge. For instance, if a .30-'06 shows primer leakage and pocket growth with a certain load combination at x CUP, then another load that is approaching the same x CUP is nearing the maximum in the same case.

Piezotransducers and strain gage measurements map the entire pressure curve and provide great insight into the internal ballistics of ammo but should not be relied upon for a specific load maximum. For instance, a load that produces x PSI and doesn't leak/shuck primers shouldn't be used to make another load based on the peak pressure of x PSI for case failure could happen at lower pressures IF the pressure curve is flatter/longer.
 
W

WESHOOT2

New member
KB Gray Area style

If all your shooting is done through Ruger revolvers pressure doesn't matter LOL.

'Cause you'll know when you went too far...............
 
Q

Quartus

New member
This is a test with great repeatability
Click to expand...


And that makes a useful test. The copper method came into being because waaayy back then it was not possible to measure PSI with any accuracy. Not at those pressures, for such a short duration. Now with piezo transducers we can see a lot more, but CUP continues to be relevant for the reasons outlined by Keith.

Twice.

:D
 
W

Waterdog

Moderator
I have seen several Rugers that were shot loose. Neanderthal friend of mine, likes having the front sight slam his forehead. I aint kiddin!

Waterdog
 
You must log in or register to reply here.
Top