CUP to PSI rough equivelent ???

Magnum Wheel Man · July 17, 2008, 10:28 AM

I'm looking at a couple of cartridges right now... ( 22 Hornet, & 5.7 X 28 )

which seem pretty close balistically... however max pressure in the Hornet is listed in CUP, & the 5.7 by PSI...

I've noticed lots of older cartridges are listed in CUP, & most of the newer cartridges in PSI...

I understand that they are very different measurement, but... is there a quick & dirty formula that can give a rough comparision between the 2 ???

BurkGlocker · July 17, 2008, 01:16 PM

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

This may help...

Scorch · July 17, 2008, 02:10 PM

Quote:

I'm looking at a couple of cartridges right now... ( 22 Hornet, & 5.7 X 28 )which seem pretty close balistically... however max pressure in the Hornet is listed in CUP, & the 5.7 by PSI...

They look "pretty close", but the 22 Hornet was developed almost 90 years ago for varminting with single shot rifles, and the 5.7X28 was developed for police use to penetrate body armor when fired from a pistol. They both launch a 35 gr bullet at close to 3000 fps, good enough for short- to medium-range varminting. One problem may arise from the 5.7X28 being a proprietary round, and I have read of people having problems with reloading it. If you want more velocity with slightly heavier bullets, the 221 Fireball is another round to consider, and it will outperform both the other rounds.

Magnum Wheel Man · July 17, 2008, 03:15 PM

WHARS... thanks for that link.... I found it extremely informative & believable...

SL1 · July 17, 2008, 03:55 PM

Bramwell's paper in that linked site uses old and new SAAMI standard values, NOT COMPARATIVE MEASUREMENTS and it leaves out pistol rounds. It is not too surprising that a group like SAAMI would pick a formula to set new stndards from old, even if it is not completely "correct" to relate the two measurements that way.

To see where some SAAMI standards do NOT fit this correlation, consider the new and old standards for the 357 magnum: 35,000 psi vs 46,000 CUP. It is WAY oof Bramwell's line. But, it also is clear that they produce different pressures, because they call for different charges of the same powders.

For another look at this comparison, consider the graph on page 43 of this link: http://deepblue.lib.umich.edu/handle/2027.42/3866 . It shows a non-linear relationship between CUP and pressure measured with a strain gauge.

SL1

wncchester · July 17, 2008, 04:29 PM

"... is there a quick & dirty formula that can give a rough comparision between the 2 ?"

No. There's not even a long, convoluted formula because it can't be done.

joneb · July 17, 2008, 06:43 PM

Quote:

... is there a quick & dirty formula that can give a rough comparision between the 2 ?"

No, it's like trying to get a Liberal Democrat to think logically, it just can't happen

brickeyee · July 17, 2008, 06:45 PM

The problem is that the older copper crusher system has significant momentum of the components and requires actual physical movement of the piston to crush the copper cylinder.
The PSI system uses piezo transducers that require essentially zero movement, eliminating the momentum problem.

The momentum problem has more of an impact on very fast pressure pulses.
If you correlate the CUP system against the PSI piezo system you get more spread than is useful for determining actual readings, and the fitted line does not go through the 0,0 point.

This means that 0 CUP does NOT equal 0 PSI(piezo).
This indicates a systemic error in the comparison, mostly due to the momentum of the anvil in the CUP measurement technique.
The CUP system could be improved, but with the advent of the piezo system and the ability to measure pressure throughout the entire barrel dwell time of the bullet (as opposed to the peak only of the CUP system) there is no reason to bother.

For a a single cartridge over a limited burn rate range the numbers can be aligned reasonably well.
For multiple cartridges over a range of pressures and burning rates the alignment is not useful.

Pistol cartridges seem to fare worse sine they tend to have faster burning powders resulting in narrower pressure pulses.
Rifle powders and cartridges tend to be better since the range of useful burning rates is more limited.

steve4102 · July 17, 2008, 07:39 PM

Denton's numbers do not work across the board. His formula has been proven to be unreliable in many cartridges.

All I can offer is what Quickload has for PSI in both the 22 Hornet and the 5.7x28.

22 Hornet(222 grove=CIP+SAAMI)--43,511psi
22 Hornet(224 grove=custom)--43,511PSI
22 K Hornet--43511psi

5.7x28FN--50,038psi

Hope this helps?

crowbeaner · July 17, 2008, 08:42 PM

At about 28,000 cup the psi is about equal. After that they take off in different directions. That level is about what trapdoor Springfields use. There is no equation to get one to correspond to the other. This is why many sources of data is a very good idea. I have some from the 60s to present.

wncchester · July 18, 2008, 04:02 PM

"Liberal Democrat" ---- Isn't that redundant?

totalloser · July 20, 2008, 10:52 PM

I hope this is not going to be used to transfer load data from one cartridge to another. That would be a VERY bad idea, absolutely destined to fail. The above information should only be considered in regards to choosing a firearm. Not for 5.7 load data. Just in case that was the thought.

PS Answer to the above; Depends on your definition of "Liberty"

July 17, 2008, 10:28 AM	#1
Magnum Wheel Man Senior Member Join Date: July 26, 2006 Location: Southern Minnesota Posts: 9,333	CUP to PSI rough equivelent ??? I'm looking at a couple of cartridges right now... ( 22 Hornet, & 5.7 X 28 ) which seem pretty close balistically... however max pressure in the Hornet is listed in CUP, & the 5.7 by PSI... I've noticed lots of older cartridges are listed in CUP, & most of the newer cartridges in PSI... I understand that they are very different measurement, but... is there a quick & dirty formula that can give a rough comparision between the 2 ??? __________________ In life you either make dust or eat dust...

July 17, 2008, 03:15 PM	#4
Magnum Wheel Man Senior Member Join Date: July 26, 2006 Location: Southern Minnesota Posts: 9,333	WHARS... thanks for that link.... I found it extremely informative & believable... __________________ In life you either make dust or eat dust...

July 17, 2008, 08:42 PM	#10
crowbeaner Senior Member Join Date: June 4, 2007 Location: Upstate SC Posts: 1,943	At about 28,000 cup the psi is about equal. After that they take off in different directions. That level is about what trapdoor Springfields use. There is no equation to get one to correspond to the other. This is why many sources of data is a very good idea. I have some from the 60s to present. __________________ If you want your children to follow in your footsteps, be careful where you walk. Beware the man that only owns one gun; he probably knows how to use it. I just hope my ship comes in before my dock rots.

July 17, 2008, 01:16 PM	#2
BurkGlocker Senior Member Join Date: May 18, 2008 Location: Sheppard AFB, TX Posts: 568	http://www.shootingsoftware.com/ftp/psicuparticle2.pdf This may help...

July 17, 2008, 03:55 PM	#5
SL1 Senior Member Join Date: November 8, 2007 Posts: 2,001	Bramwell's paper in that linked site uses old and new SAAMI standard values, NOT COMPARATIVE MEASUREMENTS and it leaves out pistol rounds. It is not too surprising that a group like SAAMI would pick a formula to set new stndards from old, even if it is not completely "correct" to relate the two measurements that way. To see where some SAAMI standards do NOT fit this correlation, consider the new and old standards for the 357 magnum: 35,000 psi vs 46,000 CUP. It is WAY oof Bramwell's line. But, it also is clear that they produce different pressures, because they call for different charges of the same powders. For another look at this comparison, consider the graph on page 43 of this link: http://deepblue.lib.umich.edu/handle/2027.42/3866 . It shows a non-linear relationship between CUP and pressure measured with a strain gauge. SL1

July 17, 2008, 04:29 PM	#6
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	"... is there a quick & dirty formula that can give a rough comparision between the 2 ?" No. There's not even a long, convoluted formula because it can't be done.

July 17, 2008, 06:45 PM	#8
brickeyee Senior Member Join Date: December 29, 2004 Posts: 3,351	The problem is that the older copper crusher system has significant momentum of the components and requires actual physical movement of the piston to crush the copper cylinder. The PSI system uses piezo transducers that require essentially zero movement, eliminating the momentum problem. The momentum problem has more of an impact on very fast pressure pulses. If you correlate the CUP system against the PSI piezo system you get more spread than is useful for determining actual readings, and the fitted line does not go through the 0,0 point. This means that 0 CUP does NOT equal 0 PSI(piezo). This indicates a systemic error in the comparison, mostly due to the momentum of the anvil in the CUP measurement technique. The CUP system could be improved, but with the advent of the piezo system and the ability to measure pressure throughout the entire barrel dwell time of the bullet (as opposed to the peak only of the CUP system) there is no reason to bother. For a a single cartridge over a limited burn rate range the numbers can be aligned reasonably well. For multiple cartridges over a range of pressures and burning rates the alignment is not useful. Pistol cartridges seem to fare worse sine they tend to have faster burning powders resulting in narrower pressure pulses. Rifle powders and cartridges tend to be better since the range of useful burning rates is more limited.

July 17, 2008, 07:39 PM	#9
steve4102 Senior Member Join Date: December 23, 2005 Location: Minnesota Posts: 2,952	Denton's numbers do not work across the board. His formula has been proven to be unreliable in many cartridges. All I can offer is what Quickload has for PSI in both the 22 Hornet and the 5.7x28. 22 Hornet(222 grove=CIP+SAAMI)--43,511psi 22 Hornet(224 grove=custom)--43,511PSI 22 K Hornet--43511psi 5.7x28FN--50,038psi Hope this helps?

July 18, 2008, 04:02 PM	#11
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	"Liberal Democrat" ---- Isn't that redundant?

July 20, 2008, 10:52 PM	#12
totalloser Senior Member Join Date: October 19, 2007 Location: Fort Bragg, CA Posts: 679	I hope this is not going to be used to transfer load data from one cartridge to another. That would be a VERY bad idea, absolutely destined to fail. The above information should only be considered in regards to choosing a firearm. Not for 5.7 load data. Just in case that was the thought. PS Answer to the above; Depends on your definition of "Liberty"