CUP><PSI ???

  • 2.4K Views
  • Last Post 19 February 2011
Fg1 posted this 14 February 2011

Ive been wondering now for a time what is with the reloading manuals switching over to PSI ratings for the pressures when all this time as long as I can remember pressures have been listed in CUP ??

I emailed Hodgdons and he explained the two methods which I already understood except the WHY switch over when CUP had been used as Guage  for choosing loads for all this time .

I also ask if there was a way to convert one to the other and the answer I got was no because of the way they were measuered !

Kinda messes up comparing loads from several books to choose a load !

Attached Files

Order By: Standard | Newest | Votes
RicinYakima posted this 15 February 2011

Yep, I struggled with this issue for years now. Finally, I just accepted load data with either system. Old powder, that I have lots of, I load to CUP. New powder I load to PSI data.

Attached Files

joeb33050 posted this 15 February 2011

From the book, 6.1

Pressure measurements made with copper or lead crushers are in COPPER UNITS OF PRESSURE = CUP, (infrequently LEAD UNITS OF PRESSURE = LUP)

Pressure measurements made with strain gauges are in  pounds per square inch = psi (or sometimes, across the water, in those baffling metric things). The Lyman handbooks report pressure in CUP, other sources use psi. To confuse the novice, thousands of pounds of pressure are sometimes abbreviated to “ksi", so 20,000 psi would become “20 ksi."

The Lyman 47th Handbook has a table of CUP and psi values for a series of cartridges (pg. 93) and says (pg. 92) “It (the table) clearly points out that it would be an error to assume any correlation between the two test methods." 

However, I found this on the Internet:

 

http://www.steyrscout.org/intballi.htm

"New statistical data analysis suggests that for most cartridges ANSI/SAAMI Maximum Average Piezo (PSI) and Maximum Average copper crusher (CUP) taken in a “standard” barrel can be related by the following formula which has an R^2 value (a statistical measurement of certainty) of .927.

(1.51586 * CUP) - 17902.0 = PSI

While the relationship is generally within Kpsi (it assumes that the CUP was determined using ANSI/ SAAMI standards) one should not rely on this conversion for absolute maximum loads." 

 

The Lyman 47th Handbook table, pg. 93, shows both CUP and psi pressures for a set of cartridges. This table was developed by the Hercules Powder Co.

 I applied the formula to the CUP pressures in the Lyman table and the formula worked pretty well.

            The left three columns in this table duplicate the Lyman table.

            “ESTIMATED PSI” shows the pressure estimated using the formula above, from the CUP values in the Lyman table.

            “ESTIMATED PSI/MEASURED PSI” shows percentage values indicating how close the estimated pressure is to the measured pressure.

            The largest percentage is 110.77% (estimated pressure was 110.77% of measured pressure), the smallest percentage was 87.65%, and average was 100.5%.  

            Given the fuzziness of chamber pressure measurements this appears to be a reasonably accurate method of converting CUP to PSI and the reverse.

Heed the warning on the Internet cite-"one should not rely on this conversion for absolute maximum loads." 

 

 

MEASURED

MEASURED

ESTIMATED

ESTIMATED PSI/

 

CUP

PSI

PSI

MEASURED PSI

22-250 Rem

53000

62000

62439

100.71%

222 Rem

46000

50000

51828

103.66%

223 Rem

52000

55000

60923

110.77%

6MM Rem

52000

65000

60923

93.73%

243 Win

52000

60000

60923

101.54%

25-06 Rem

53000

63000

62439

99.11%

257 Roberts

45000

54000

50312

93.17%

257 Roberts +P

50000

58000

57891

99.81%

270 Win

52000

65000

60923

93.73%

7MM-08 Rem

52000

57500

60923

105.95%

7X57 Mauser

46000

51000

51828

101.62%

7MM Rem Mag

52000

61000

60923

99.87%

280 Rem

50000

60000

57891

96.49%

30 Carbine

40000

40000

42732

106.83%

30-06 Spr.

50000

60000

57891

96.49%

30-30 Win

38000

42000

39701

94.53%

300 Savage

46000

47000

51828

110.27%

300 Win Mag

54000

64000

63954

99.93%

303 British

45000

49000

50312

102.68%

308 Win

52000

60000

60923

101.54%

8X57 Mauser

37000

35000

38185

109.10%

8MM Rem Mag

54000

65000

63954

98.39%

338 Win Mag

54000

64000

63954

99.93%

35 Rem

35000

33500

35153

104.93%

45-70 Gov't.

28000

28000

24542

87.65%

Attached Files

Ed Harris posted this 15 February 2011

There is no conversion application of a correction factor between the two types of measurements which is safe.

There are differences between Government and SAAMI procedures both in radial copper and in piezo-electric.

Under SAAMI procedure piston hole in the barrel is located farther forward on the case body because the case is not drilled and a conformal transducer of Kistler type is used.

Under NATO and US government procedure the case is drilled, the hole covered with Teflon tape and the hole oriented to the transducer. The purpose of this is to mitigate against the effects of changes in case wall material and thickness, which affect the pressure readings received by the transducer.

Drilling the case avoids variations in the measurement caused by different case materials, thickness or state of anneal, but there is always some gas leakage around the piston hole.

SAAMI procedure is better suited for production because cases do not have to be drilled, taped and oriented.  The chamber stays cleaner because you don't have gas leakage around the piston hole, but conformal transducers require much more effort in to maintain them in calibration. 

So you have an apples and prunes situation depending upon whether the gage uses Kistler or BRL minihat type of transducer.

There are similar differences in government and SAAMI gages in the radial copper method, the government barrel using a drilled case and .225x.400 size “C” copper with no gascheck between the piston and the cartridge case, whereas SAAMI procedure used a more sensitive .225x.500 copper and a wax filled gascheck sandwiched between the piston and undrilled cartridge case.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

Attached Files

joeb33050 posted this 15 February 2011

Ed Harris wrote: There is no conversion application of a correction factor between the two types of measurements which is safe. Well this is certainly not true. For pressures, say, below 40kp in strong bolt guns, the conversion relationship given above is perfectly safe to use. Why one would want to know the pressure escapes me, but certainly for the data I compared, there's no risk at pressures below some ?? number.Now, I could be dead wrong, and will be happy to see any data that Ed has to support his contention. Absent that data, I think the conversion formula is roughly correct.  There are differences between Government and SAAMI procedures both in radial copper and in piezo-electric.

Under SAAMI procedure piston hole in the barrel is located farther forward on the case body because the case is not drilled and a conformal transducer of Kistler type is used.

Under NATO and US government procedure the case is drilled, the hole covered with Teflon tape and the hole oriented to the transducer. The purpose of this is to mitigate against the effects of changes in case wall material and thickness, which affect the pressure readings received by the transducer.

Drilling the case avoids variations in the measurement caused by different case materials, thickness or state of anneal, but there is always some gas leakage around the piston hole.

SAAMI procedure is better suited for production because cases do not have to be drilled, taped and oriented.  The chamber stays cleaner because you don't have gas leakage around the piston hole, but conformal transducers require much more effort in to maintain them in calibration. 

So you have an apples and prunes situation depending upon whether the gage uses Kistler or BRL minihat type of transducer.

There are similar differences in government and SAAMI gages in the radial copper method, the government barrel using a drilled case and .225x.400 size “C” copper with no gascheck between the piston and the cartridge case, whereas SAAMI procedure used a more sensitive .225x.500 copper and a wax filled gascheck sandwiched between the piston and undrilled cartridge case.

Attached Files

Ed Harris posted this 15 February 2011

The government labs, CIP and SAAMI all agree on this based upon their collective  experience.  If you disagree with that conclusion I recommend that you take it up with them. I am only the messenger.

I am not a qualified as a subject matter expert in this area.  I only worked in the firearms industry for 14 years, and have been out of it for the last 20, so I am not fully knowledgeable of current procedures and standards. In the 1980s I worked in private and government labs firing thousands of rounds of military ammunition from 5.56-40mm and sporting ammunition in foreign technical intelligence, R&D and production QA environments.  The results obtained using different test methods were never deemed comparable under any circumstances and and required different procedures and calibration standards. 

That in itself could be interpreted as an apparent clue. 

If you wish to make independent interpretations and develop load data based upon educated guesses I recommend extreme caution and would wish you good luck in your endeavors. 

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

Attached Files

Fg1 posted this 15 February 2011

Thank you all for your input on this . This is what bugs me about this as does the metric system ! Something that works well and is in use and accepted by the end users as a very usefull tool in their application ............why change the tool ? Make it look similar to the one you have been using for 40 years or better in some cases , but have it react differently and possibly dangerously in actual use ! Makes perfectly good sence to me ! If it works good chuck it out and get something new you are totally unfamiliar with to burn your time and energy up with instead of doing what you enjoy !

Attached Files

joeb33050 posted this 18 February 2011

Ed;

While you contend that “The government labs, CIP and SAAMI all agree on this, (There is no conversion application of a correction factor between the two types of measurements which is safe.)  based upon their collective  experience."; I can't find and thus don't know that that agreement exists.

Let us look at your, (and Lyman's) contention.

 

We have pressure in the chamber of a gun.

We have two methods of measuring that pressure under discussion, copper crusher and piezoelectric. (Strain gage methods?)

If the contention is true, that there is no mathematical conversion method between the two, then one or both of the methods of measurement must be incorrect. N'est pas?

 

However, the contention seems to be untrue. See

http://kwk.us/pressures.html , and in particular the links.

I found Denton Bramwell's article very interesting .

Note the frequent warnings not to use and rely on any conversion formula at the upper pressure areas. This takes care of the “...which is safe.” element of the contention.

Then we have available several different conversion formulas with more than convincing r^2s that, if the user complies with the warning,  provide safe and reasonably accurate conversions.

But wait, there's more.

SAAMI sets voluntary pressure standards for manufacturers, (see the link on the cite); and manufacturers are instructed to use a random sample size of 10 cartridges from a lot to measure pressure. These SAAMI pressure standards are set with at least the strength of the cartridge case and commonly used guns in mind. There seems no objective test involved in the selection of these standards.

 

Now a sample size of 10 and the recently-recognized problems with randomness suggest to me that any AVERAGE SAMPLE pressure measured is not a precise estimator of the POPULATION pressure. Then, for a cartridge such as the 342 Knurlman, SAAMI copper crusher pressure and piezoelectric sample pressure measurements are by absolutely not precise estimators of average pressure, meaning that the published CUP and PSI pressures are not precise. This is just part of every estimation system, not merely SAAMI, who I'm sure are doing a great job. Now, since the published pressures have variation within them, any conversion formula will be inexact because the SAAMI data is inexact.

If we set two guys up picking up rocks and estimating the weight of each rock by hand, one in pounds and the other in kilograms; then we should not be surprised to find that developing a conversion formula from pounds to kilograms shows some error. However, there is a clear and precise relationship between pounds and kilograms.

 

It should be noted that the conversion formula creators all make this assumption: CIP and SAAMI both set a pressure limit for a cartridge in some fashion. Then, (when they provide data for both CUP and PSI), cartridges yielding the set pressure are tested using the other method. If CUP pressure has been decided on at CC,CCC , then cartridges producing CC,CCC must be produced and then tested, yielding pressure of PP,PPP.

We assume but do not know that that has happened.     

joe b.

Ed Harris wrote: The government labs, CIP and SAAMI all agree on this based upon their collective  experience.  If you disagree with that conclusion I recommend that you take it up with them. I am only the messenger.

I am not a qualified as a subject matter expert in this area.  I only worked in the firearms industry for 14 years, and have been out of it for the last 20, so I am not fully knowledgeable of current procedures and standards. In the 1980s I worked in private and government labs firing thousands of rounds of military ammunition from 5.56-40mm and sporting ammunition in foreign technical intelligence, R&D and production QA environments.  The results obtained using different test methods were never deemed comparable under any circumstances and and required different procedures and calibration standards. 

That in itself could be interpreted as an apparent clue. 

If you wish to make independent interpretations and develop load data based upon educated guesses I recommend extreme caution and would wish you good luck in your endeavors. 

Attached Files

cityboy posted this 18 February 2011

Joe

What you fail to understand is that there are two totally different technologies involved and trying to relate one to the other is a lost cause.

You just don't know what you are talking about.

Jim

Attached Files

James Ball posted this 19 February 2011

How bout we settel it,the first one to blow his gun up looses.

Attached Files

joeb33050 posted this 19 February 2011

cityboy wrote: Joe

What you fail to understand is that there are two totally different technologies involved and trying to relate one to the other is a lost cause.

You just don't know what you are talking about.

Jim Jim;

What you fail to understand is that several fairly bright and experienced men have looked into the matter and come up with conversion formulas that come extremely close to matching the data available. I think the lost cause is attempting to get those with closed minds to read the cites and the links within the cites. Certainly opinion is more important than data.

You just don't know what I'm talkinjg about.

joe b.

Attached Files

joeb33050 posted this 19 February 2011

James Ball wrote: How bout we settel it,the first one to blow his gun up looses.

One of the many thing I don't understand is how and/or why anyone uses published pressure data in the reloading process. Could you or someone explain this? I don't want to blow another gun up.

joe b.

Attached Files

James Ball posted this 19 February 2011

The differ between the two in my opinion,one measures pressure spread,the other measures,pressure speed,shock speed.I have only had one misshap, double charge of red dot in a 303brit with a 200 gr bullet,cracked one lug on the bolt.But have found that most guns,(bolt Type)will handle more than( reason)loads.If you watch for the signs,frosting case,primmer flattening,primmer backing out,ect. you should not have any prob.Most bolt guns will handle (with heavy Barrel)way more than published cup or psi.James Ball

Attached Files

Close