» Advanced

Go Back   Shooters Forum > Handloading > Handloading Procedures/Practices
Register FAQ Members List Donate Calendar Search Today's Posts Mark Forums Read



Reply
 
LinkBack Thread Tools Rate Thread Display Modes
  #1  
Old 01-24-2004, 02:25 PM
Ranch Dog's Avatar
Beartooth Regular
 
Join Date: Oct 2003
Location: Cuero, TX
Posts: 3,484
CUP vs. PSI


Registered Users do not see the above ad.


Has anyone a formula for converting CUP to PSI?
__________________
Michael
Reply With Quote
  #2  
Old 01-24-2004, 02:52 PM
MikeG's Avatar
The Hog Whisperer (Administrator)
 
Join Date: Jan 2001
Posts: 27,338
'Taint none.

This was discovered after electronic pressure-testing equipment came into widespread use.

Bottom line is, copper crusher measurements are somewhat approximate and don't necessarily get the actual peak pressure.

Obviously, they worked well for many years, and beat guessing, but that's also a reason to not push the envelope and be glad that there is a certain strength factor built into guns to help prevent disaster with a slight overload.
__________________
MikeG

Quote:
Originally Posted by faucettb
Welcome to the forum. Rules are simple, be nice and join in.
Reply With Quote
  #3  
Old 01-24-2004, 04:05 PM
Moderator
 
Join Date: Dec 2002
Location: Jefferson Parish (via N.O.)
Posts: 9,035
There isn't one...not even a good aproximation.
Reply With Quote
  #4  
Old 01-24-2004, 05:23 PM
Ranch Dog's Avatar
Beartooth Regular
 
Join Date: Oct 2003
Location: Cuero, TX
Posts: 3,484
Thanks guys... that is what I thought. That was my answer on another site, even gave an explaination why but some still say there is a formula. This is what I understand...

When the Copper Units of Pressure was established the reference medium was a standard size plug of copper that was placed in the crusher. The results of the pressure was referenced to the change of this medium.

PSI does not use a reference medium but the pressure developed within the individual cartridge chamber dimensions. That dimension and it's volume is the base or reference for the pressure test. That base or reference is different for every cartridge tested and must be established for the testing to begin. Because each cartridge is different, there is not a constant to convert all the different cartridges that have established CUPs. They all must be developed individually.
Reply With Quote
  #5  
Old 01-24-2004, 07:22 PM
The Troll Whisperer (Moderator)
 
Join Date: Jan 2003
Location: Mesa, Arizona
Posts: 19,872
I believe you hit the nail right on the head. PSI relates to chamber expansion, CUP to the compression of a copper plug.

I suppose some egghead mathematician physicist could correlate the driving of a piston into a copper slug to the expansion ratio and stress on a chamber into some sort of comparative formula, but it ain't gonna be me!
__________________
NRA Benefactor Member
NRA Certified Police Firearms Instructor
NRA Certified Range Safety Officer
NAHC Life Member

"Firearms only have two enemies - rust and politicans" author unknown
Reply With Quote
  #6  
Old 01-24-2004, 08:32 PM
Beartooth Regular
 
Join Date: Dec 2000
Posts: 1,182
The funny part is that they used to express the Crusher results in PSI. Then when Piezo systems started coming into use, to avoid confusion, started expressing Crusher results in "CUP". However, one does not correspond to the other as stated above.

Be attentive when reading older load data in magazines and such up until the late sixties, early seventies or so expressed in PSI, before the change.

Piezo systems (Transducer) measure peak pressures, rate of buildup and also pressure DURATION on an oscilliscope or computer monitor.

This explains some downgrading of loads, among other reasons, in some newer loading manuals. Like Speer with the 357 mag loadings.

Regards
__________________
Send a Care Package to Our Troops Overseas Click Here

Last edited by Contender; 01-24-2004 at 08:40 PM.
Reply With Quote
  #7  
Old 01-24-2004, 08:59 PM
Jack Monteith's Avatar
Beartooth Regular
 
Join Date: Dec 2000
Location: Saskatchewan
Posts: 7,788
It doesn't take an egghead mathematician physicist to figure a formula, `cause I did it. Try C.U.P. X 1.498 - 17148 = P.S.I. I ran a quick linear regression on the numbers in the 1992 Hercules Reloaders Guide and came up with this chart. Only problem is, the errors are pretty big. The third column, VALUE, is the calculated PSI and the ERROR is VALUE - actual PSI. Looking at the .270 and 7-08 numbers, where the errors are large and in opposite directions has me doubting if a higher order regression will improve the formula.

Bye
Jack


CUP PSI VALUE ERROR
53000 62000 62259 259 .22-250 Remington
46000 50000 51771 1771 .222 Remington
52000 55000 60761 5761 .223 Remington
52000 65000 60761 -4239 6mm Remington
52000 60000 60761 761 .243 Winchester
53000 63000 62259 -741 .25-06 Remington
45000 54000 50273 -3727 .257 Roberts
50000 58000 57764 -236 .257 Roberts + P
52000 65000 60761 -4239 .270 Winchester
52000 57500 60761 3261 7mm-08 Remington
40000 45000 42782 -2218 7-30 Waters
46000 51000 51771 771 7 x 57 Mauser
52000 61000 60761 -239 7mm Remington Magnum
50000 60000 57764 -2236 .280 Remington
40000 40000 42782 2782 .30 Carbine
50000 60000 57764 -2236 .30-06 Springfield
38000 42000 39785 -2215 .30-30 Winchester
46000 47000 51771 4771 .300 Savage
54000 64000 63757 -243 .300 Winchester Magnum
45000 49000 50273 1273 .303 British
52000 60000 60761 761 .308 Winchester
37000 35000 38287 3287 8mm Mauser
54000 65000 63757 -1243 8mm Remington Magnum
54000 64000 63757 -243 .338 Winchester Magnum
35000 33500 35291 1791 .35 Remington
28000 28000 24803 -3197 .45-70 Government
Reply With Quote
  #8  
Old 01-24-2004, 09:06 PM
Beartooth Regular
 
Join Date: Dec 2000
Posts: 1,182
Isn't it what amounts to the lower pressure ranges below around 40,000 tend to be similar, then as they climb the "divergence" becomes more pronounced?

Jack, you're outta control
__________________
Send a Care Package to Our Troops Overseas Click Here
Reply With Quote
  #9  
Old 01-24-2004, 09:25 PM
MikeG's Avatar
The Hog Whisperer (Administrator)
 
Join Date: Jan 2001
Posts: 27,338
Quote:
Originally Posted by Contender

This explains some downgrading of loads, among other reasons, in some newer loading manuals. Like Speer with the 357 mag loadings.

Regards

Oh my yes.... saw a used (older) Speer manual in a second-hand bookstore once, there were some eye-ball popping loads listed for the .357 mag... most of which I wouldn't shoot in my Blackhawks, much less a Smith!
__________________
MikeG

Quote:
Originally Posted by faucettb
Welcome to the forum. Rules are simple, be nice and join in.
Reply With Quote
  #10  
Old 01-25-2004, 01:03 AM
Beartooth Regular
 
Join Date: Nov 2003
Location: Fallon Nevada
Posts: 184
Wrong!
I think somebody has confused the (excellant, within its limitations) Personal Balistics Laboratory with piezoelectric pressure transducers. Piezo transducers no more need the chamber dimensions apriori than you need the tire size when you measure the air pressure in your tires; pressure is pressure, no matter how big or little the bottle is. 35 psi is still 35 psi when it's in my pickup tires or my sportcar's tires. The difference is, how fast can the guage react? The electronic guage can react much more quickly, doesn't have as much overshoot.

CUP: Copper Units of Pressure. A little steel piston is exposed to chamber pressure and is used to shorten (crush) a copper pellet. The balististian hopes that the inertia of the piston won't affect his measurement. He also hopes the lot of copper pellets is uniform enough to give him good data. They're calibrated by applying known pressures to one or several of the copper pellets and measureing how much they were shortened. They can then generate a tarage chart from the amount. When they shoot their pressure data, they compare the length of the pellet to the tarage chart to get the pressure. Obviously, each pellet can only be used once. Also, the process is rife with both random errors and systematic errors.

PSI: on the other hand, we can replace the piston and copper with a quartz crystal and attach electrodes to it. No physical inertia of a piston to worry about. The pressure transducer is reusable until you're sick of it. You avoid the calibration problems because, once your crystal is calibrated (volts out in response to pressure) you don't keep replacing your transducer so you don't have to just hope that it responds the same as the one you calibrated with. So you get more accurate, more repeatable results. Not only that, but you get an electronic time-history of the pressure so you can see how the pressure evolves over time!

I seriously doubt the improved pressure measurement caused the balistic labs to reduce their recommended powder charges. That would be like getting a more accurate tire guage and finding you need to change your tire pressure because of the different guage. No, you are more likely to reduce your tire pressure because you're wearing the centers of your tires faster than the outsides. Similarly, people were probably running into problems using the higher powder charges. After all, the bullet manufacturers didn't start actual pressure testing until quite recently because it was too expensive. The switch to piezo gear greatly reduced the costs of shooting pressure data and, thereby, conforming to SAAMI specs.

-91
Reply With Quote
  #11  
Old 01-25-2004, 07:28 AM
John Kort's Avatar
Beartooth Regular
 
Join Date: Mar 2001
Location: Erie, PA
Posts: 538
C.U.P. and P.S.I. relationship values seem to vary in different cartridges. Here are two examples from the Accurate Smokeless Powders Loading Guide Number 2:


SAMMI maximum average pressure for the:
.30-30 - 42,000 psi / 38,000 cup
.308 - 62,000 psi / 52,000 cup

John
__________________
aka w30wcf
aka w44wcf (black powder)
aka Jack Christian SASS #11993" I can do all things through Christ who strengthens me." Philippians 4:13
Reply With Quote
  #12  
Old 01-25-2004, 10:33 AM
IDShooter's Avatar
Beartooth Regular
 
Join Date: Apr 2001
Location: North Idaho
Posts: 2,076
To complicate things even further, there are lots of different ways of measuring pressure with a transducer - in the chamber itself, as in the SAAMI protocols; at the chamber mouth, as in European protocols; and with the transducer glued to the outside of the barrel, as in the home ballistics labs. All can give accurate results, but they will be different from one another unless calibrated.
__________________
IDShooter

"Whenever you find yourself on the side of the majority, it is time to pause and reflect." - Mark Twain
Reply With Quote
  #13  
Old 01-25-2004, 10:48 AM
The Troll Whisperer (Moderator)
 
Join Date: Jan 2003
Location: Mesa, Arizona
Posts: 19,872
Ooooooooh - you guys are giving me a pressure headache!

This is why I tend to buy almost every reloading manual's latest editions. Figure if I stick with their current loadings with current powders and bullets, I can't go too far wrong. This, of course doesn't affect those tried and found true personal loadings developed over the years.

Being older now and not quite as adventuresome as years past, the published data and the old proven loads are plenty good enough for me. The few wildcats in the vault had loads very carefully developed on the conservative end to start and finished with those of best accuracy, regardless of velocity loss.
__________________
NRA Benefactor Member
NRA Certified Police Firearms Instructor
NRA Certified Range Safety Officer
NAHC Life Member

"Firearms only have two enemies - rust and politicans" author unknown
Reply With Quote
  #14  
Old 01-25-2004, 11:08 AM
Moderator
 
Join Date: Dec 2002
Location: Jefferson Parish (via N.O.)
Posts: 9,035
There is a lot to be said for using a caliber that will give the performance you want without having to run up against the absolute max. pressure allowed.
Reply With Quote
  #15  
Old 01-25-2004, 02:21 PM
MikeG's Avatar
The Hog Whisperer (Administrator)
 
Join Date: Jan 2001
Posts: 27,338
Quote:
Originally Posted by 91Carcano

I seriously doubt the improved pressure measurement caused the balistic labs to reduce their recommended powder charges. That would be like getting a more accurate tire guage and finding you need to change your tire pressure because of the different guage. No, you are more likely to reduce your tire pressure because you're wearing the centers of your tires faster than the outsides. Similarly, people were probably running into problems using the higher powder charges. After all, the bullet manufacturers didn't start actual pressure testing until quite recently because it was too expensive. The switch to piezo gear greatly reduced the costs of shooting pressure data and, thereby, conforming to SAAMI specs.

-91
I think in Speer's case, it wasn't 'improved' pressure testing that caused them to reduce their loads, it was the fact that they started using ANY pressure testing.

Anyway, nice summary.
__________________
MikeG

Quote:
Originally Posted by faucettb
Welcome to the forum. Rules are simple, be nice and join in.
Reply With Quote
  #16  
Old 01-25-2004, 05:01 PM
Beartooth Regular
 
Join Date: Dec 2000
Posts: 1,182
Quote:
--------------------------------------------------------------------------------
Originally Posted by 91Carcano


I seriously doubt the improved pressure measurement caused the balistic labs to reduce their recommended powder charges. That would be like getting a more accurate tire guage and finding you need to change your tire pressure because of the different guage. No, you are more likely to reduce your tire pressure because you're wearing the centers of your tires faster than the outsides. Similarly, people were probably running into problems using the higher powder charges. After all, the bullet manufacturers didn't start actual pressure testing until quite recently because it was too expensive. The switch to piezo gear greatly reduced the costs of shooting pressure data and, thereby, conforming to SAAMI specs.

-91
--------------------------------------------------------------------------------




Excerpted Verbatim from Speer #12:

Introduction to handgun data,

"When relatively quick burning propellants are used, the transducer picks up early pressure readings that contribute to total pressure. The result is that charge weights of quick burning propellants will usually be LESS on data developed on a transducer system than in data developed on a crusher system. This effect has led us to show more powders having a moderate burning rate. Loads using Bullseye, 231 and similar powders may BE LESS THAN SHOWN IN OLDER SPEER MANUALS."

and

"The transducer system favors some cartridges more than others. We were able to improve upon the performance of the 44 Special and 9mm Luger compared to past manuals. HOWEVER, LOADS FOR THE 357 MAGNUM ARE DEFINATELY DOWN. The transducer limit is 35,000 PSI. The current crusher limit for the same cartridge is 45,000CUP. The difference means many of the 357 Magnum loads are LESS than shown before, although the slow burning propellants such as 296,H110 and VV N110 gave very good velocities."


Regards
__________________
Send a Care Package to Our Troops Overseas Click Here

Last edited by Contender; 01-25-2004 at 05:04 PM.
Reply With Quote
  #17  
Old 01-25-2004, 06:15 PM
Jack Monteith's Avatar
Beartooth Regular
 
Join Date: Dec 2000
Location: Saskatchewan
Posts: 7,788
Some discussion on Pressure Measurement, courtesy of Fr. Frog.
http://www.steyrscout.org/intballi.htm

Bye
Jack
Reply With Quote
  #18  
Old 02-21-2004, 05:56 PM
Beartooth Regular
 
Join Date: Dec 2003
Location: Thayer, Missouri
Posts: 160
One reason for the difference in CUP pressure and PSI pressure is that in the CUP system the pressure actually has to blow out a piece of case wall before it began to compress the copper cylinder. Older model calibers were made for much lower pressures and used thinner cases therefore it took less presssure to pierce case walls.

I believe that is why modern higher pressure cartridges show more disparity between CUP and PSI. Look at it as though the 'pressure' being measured is what is left after piercing the case wall. That also helps explains the difference between American and European methods in that the Europeans pre-pierced the case before inserting it into pressure gun and, sure enough, their system usually gives higher 'indicated' pressure levels than does the US system.

Quote:
Originally Posted by John Kort
C.U.P. and P.S.I. relationship values seem to vary in different cartridges. Here are two examples from the Accurate Smokeless Powders Loading Guide Number 2:


SAMMI maximum average pressure for the:
.30-30 - 42,000 psi / 38,000 cup
.308 - 62,000 psi / 52,000 cup

John
Reply With Quote
  #19  
Old 02-25-2004, 05:31 AM
OldWolf's Avatar
Beartooth Regular
 
Join Date: Feb 2004
Location: North Carolina
Posts: 459
FYI...

Conformal Sensor Measures
Ammunition Pressure
Through Shell Case


http://www.sensorsmag.com/articles/0...p93/main.shtml
__________________
Regards,
OldWolf
Reply With Quote
  #20  
Old 03-13-2008, 04:44 PM
Rev Rev is offline
Beartooth Regular
 
Join Date: Mar 2008
Posts: 117
If one is measuring ambient temperature, he could use a spring type thermometer (least accurate), an alcohol thermometer (more accurate), or a mercury thermometer (still more accurate), or probably many other heat sensors. The many types of thermometers are still measuring the same thing, temperature. To complicate matters, these temperatures could be expressed in different ways. I.E., absolute, centigrade (Celcius), Fahrenheit or some others of which I'm not aware. These devices and expressions are still attempts to measure the same thing. Some are more accurate than others. The measurements might be expressed in different ways.....

To say that these measurements don't correspond mathematically is just ludicrous in my opinion. How can they not correspond when measuring the same entity? Over simplification, maybe? I believe some of us are confusing more obsolete methods (with inherent inaccuracy) with more modern methods (with more inherent accuracy) with non correspondence of the data obtained.

Rev
Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On



All times are GMT -8. The time now is 07:54 AM.

< Contact Us - Shooters Forum - Archive >

 
 

All Content & Design Copyright © 1999-2002 Beartooth Bullets, All Rights Reserved
View Privacy Policy | Contact Webmaster | Legal Information
Website Design & Development By Exbabylon Internet Solutions
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.0 PL2