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Thread: PSI vs LUP

  1. #1
    Boolit Master
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    PSI vs LUP

    What's up with Lyman shotshell data showing pressure in LUP instead of PSI ?

  2. #2
    Boolit Grand Master



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    LUP is/was used for lower pressure loads than CUP before pressure transducers became common.
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  3. #3
    Boolit Grand Master

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    LUP (lead units of pressure) and CUP (copper units of pressure) use a special chamber with a hole drilled though and a piston/plunger fitted with a lead or copper slug of precise hardness and dimensions behind it. When the cartridge is fired the chamber pressure acts on the piston which compresses the slug. The slug is then measured to determine the chamber "pressure" in LUP or CUP.

    Probably more than you wanted to know!

    As M- Tecs said, this was how it was done before pressure transducers. However, many thousands of recipes were tested this way at great cost and effort so those results won't likely be abandoned any time soon.

    As powders and components change, new recipes will likely be in PSI.

    Longbow

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    Boolit Master
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    Thanks you guys,

  5. #5
    Boolit Grand Master

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    If you Google you will find conversion formulas and calculators for CUP to PSI but they will be approximate and I believe the numbers generated by each system are not linear relationships. LUP/CUP use the crusher system so there are variables in the deformation of the crushers plus both materials work harden so more deformation = more work hardening which would likely affect higher pressures results.

    I do not see any conversion for lead units of pressure.

    There is also the dwell time at pressure as both lead and copper will creep under load so a fast pressure spike may (likely does) result in less deformation of the crusher than a longer pulse at same pressure.

    The strain gauge systems measure the minute elastic expansion of the chamber, so a hoop stress, no permanent deformation like with a crusher. These have to be calibrated quite accurately though and from what I am told, many people with pressure trace systems either are not aware or do not calibrate correctly/accurately enough to get dependable results. Good for comparison maybe but not precise pressures. I know a guy who is getting shotshell loads pressure tested by Tom Armbrust for that very reason... he has seen amatuer results that show far different pressures than published/professional tests show.

    Longbow

  6. #6
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    LUP works better for very low pressure than the piezoelectric strain gauge does, which may be why they use the older LUP system versus the more modern Piezo system for shot shells. Plus, it is often cheaper to use up what you have before you buy new.
    Last edited by rintinglen; 12-08-2023 at 12:02 PM.
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  7. #7
    Boolit Mold
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    All chamber pressure measuring systems require calibration. SAAMI requires what is referred to as "Reference Standard" ammunition to be fired through the test fixture to calibrate it. That ammo is only available to SAAMI member companies and is loaded by very select labs to produce the Reference Standard ammo to include a temperature table for adjusting the pressure to the local conditions that the ammo is fired under. Very highbrow science stuff.
    You and I don't have access to RF ammo but we need to calibrate (I have a Pressure Trace II) with something. I use a tested load with pressure from the Hodgdon’s Manual that is in the middle of the burn rate of the powders loaded in that caliber. In 375 Ruger that is WW760 as there are faster and slower powders tested and WW760 I can get. It helps when that powder has been produced since the 1970's. In 300WM it is IMR4831. Haven't done my Ruger #3 in 45/70 but I will use H4198 if I can find it with the Speer 400gr FN Hotcore. It is important to duplicate the load exactly down to the COAL.
    Hope you didn't fall asleep reading this but I love this kind of minutiae.

    KB

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  8. #8
    Boolit Grand Master


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    I am a long time user of the Oehler M43 system and in the last several years, the Pressure Trace II system also. Over the last 15+ years I have, litterally, tested thousands of different loads of numerous different cartridges.

    Quote Originally Posted by longbow View Post
    If you Google you will find conversion formulas and calculators for CUP to PSI but they will be approximate and I believe the numbers generated by each system are not linear relationships. LUP/CUP use the crusher system so there are variables in the deformation of the crushers plus both materials work harden so more deformation = more work hardening which would likely affect higher pressures results.

    The copper or lead test pellet are used only once, ergo they do not "work harden".

    I do not see any conversion for lead units of pressure.

    There are no reliable "conversion" factor(s) to convert or compare the pressure measurements of CUP/LUP to that of piezo/strain gauge psi measurements. The conversion factors found on Google and from such other sources perhaps may be considered reliable only for the cartridge used, the specific components used and if tested in the same firearm/test fixture.

    There is also the dwell time at pressure as both lead and copper will creep under load so a fast pressure spike may (likely does) result in less deformation of the crusher than a longer pulse at same pressure.

    The strain gauge systems measure the minute elastic expansion of the chamber, so a hoop stress, no permanent deformation like with a crusher. These have to be calibrated quite accurately though and from what I am told, many people with pressure trace systems either are not aware or do not calibrate correctly/accurately enough to get dependable results. Good for comparison maybe but not precise pressures. I know a guy who is getting shotshell loads pressure tested by Tom Armbrust for that very reason... he has seen amateur results that show far different pressures than published/professional tests show.

    What you have been told is incorrect. A piezo system actually used a strain gauge. That system can be calibrated with special pressure equipment which is very costly and time consuming. Strain gauge systems such as the Oehler M43 and Pressure Trace II systems cannot be "calibrated" as such by the user. The strain gauges are "calibrated" when manufactured and are supplied with a factor for the specific gauge that is input into the software for the specific gauge used.

    The use of "reference ammunition" is also used to get an "offset" factor. While SAAMI Reference Ammunition is not available to non-SAAMI members the use of factory ammunition or a load with known psi measurement can be effectively used. The use of such reference ammunition does not reset anything in the measuring system or software. The conversion factor is simply used to convert the measured pressure measurement into what is presumed to be the actual psi. That's how the factories use reference ammunition and it's how I use it.


    Longbow
    Larry Gibson

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  9. #9
    Boolit Master
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    Quote Originally Posted by Kennibear View Post
    All chamber pressure measuring systems require calibration. SAAMI requires what is referred to as "Reference Standard" ammunition to be fired through the test fixture to calibrate it. That ammo is only available to SAAMI member companies and is loaded by very select labs to produce the Reference Standard ammo to include a temperature table for adjusting the pressure to the local conditions that the ammo is fired under. Very highbrow science stuff.
    You and I don't have access to RF ammo but we need to calibrate (I have a Pressure Trace II) with something. I use a tested load with pressure from the Hodgdon’s Manual that is in the middle of the burn rate of the powders loaded in that caliber. In 375 Ruger that is WW760 as there are faster and slower powders tested and WW760 I can get. It helps when that powder has been produced since the 1970's. In 300WM it is IMR4831. Haven't done my Ruger #3 in 45/70 but I will use H4198 if I can find it with the Speer 400gr FN Hotcore. It is important to duplicate the load exactly down to the COAL.
    Hope you didn't fall asleep reading this but I love this kind of minutiae.

    KB

    Sent from my SM-A326U using Tapatalk
    Ah Watch any of that have to do with shotshells?
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  10. #10
    Boolit Grand Master


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    I have measured the psi of some 410 shotshells.
    Larry Gibson

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    ― Nikola Tesla

  11. #11
    Boolit Grand Master

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    Larry:

    I probably should have said "strain hardening" and yes it does happen. Copper strain hardens as it deforms and the poiint is that at a low pressure the deformation is small so the strain hardening is small, at higher perssure the deformation is larger so the strain hardening is larger. The net result is a non-linear relationship to deformation and yield strength. This strain hardening takes place from start of deformation to end of deformation. I know the crushers are not re-used and did not mean to imply that they were and the "work" hardening was due to multiple uses. Poor terminology on my part.

    As for the rest, I was talking to a knowledgeable friend who is now having loads prefessionally pressure tested and he told me about the standards and methods. Not sure if he was referring driectly to SAAMI standards but looking at the pressure testing methods and standards in the SAAMI spec they have sections on calibration and use of reference ammunition for calibration of equipment so similar if not the same procedures.

    I would agree that as long as you have a load that produces a known pressure then that sets your standard. Where do you get that load? Results in manuals often show significant deviation for same load components and powder charge.

    I have no personal experience with pressure testing so will refrain from any further comment or speculation.

    Longbow

  12. #12
    Boolit Grand Master


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    "Not sure if he was referring driectly to SAAMI standards but looking at the pressure testing methods and standards in the SAAMI spec they have sections on calibration and use of reference ammunition for calibration of equipment so similar if not the same procedures."

    Is there a disagreement here? When I started measuring pressures I carefully read and studied the SAAMI procedures and I made/make every attempt to follow those SAAMI methods and standards as close to and as practically possible as I can. There was nothing in the SAAMI specifications regards to "calibrating" strain gauges such as is used on the M43 and Pressure Trace systems. As previously mentioned, the strain gauges are "calibrated" after manufacture and come with a "factor" [specific to that strain gauge] that is entered into the software. Also, other factors are entered for the barrel dimensions, chamber dimensions and composition with both systems. I suppose that could be considered "calibration".

    The "calibration" of a piezo-transducer fixture is akin to resetting the measurement readout to a known pressure level. Similarly, adjustment of the measured pressure is accomplished through the use of reference ammunition to obtain an offset figure to then calculate and adjust the measured pressure to be in line with the "standard" for the "reference" cartridge. This is because even the "calibrated" test fixtures of various ammunition manufacturers are different with different barrels and chambers including wear from different round counts and, thus, most often will give different pressures with the same ammunition even though they are "calibrated". Hence the "reference" ammunition offset figure is then used to then bring the "calibrated" fixture measurements to agree with the "standard". Note also SAAMI has a method for measuring the pressures of non SAAMI cartridges for which there are no SAAMI standards.

    Some also will say "The pressures you measure are only applicable to the gun you test them in." That is true. But then also, the same applies to the pressures measured by manufacturers which are then only applicable to the test fixture barrels they were tested in. That is why there are three levels of acceptable pressures in SAAMI standards for each cartridge. It is also why most many manufacturers also use strain gauge systems [Mostly Oehler M83s] on commercial firearms to validate production ammunition.

    "I would agree that as long as you have a load that produces a known pressure then that sets your standard. Where do you get that load? Results in manuals often show significant deviation for same load components and powder charge."

    I used to have contacts at Winchester and Federal that would email me their pressure measurements for different lots of cartridges. I would buy a box of Winchester or Federal cartridges and email them the product number and the lot numbers. They would then email back their own pressure measurement for the specific lot of the cartridges. That is used as "reference" ammunition. "Reference ammunition" used by SAAMI is simply a specific lot of commercially produced ammunition known for its consistency of pressure measurements. Unfortunately, the contacts I had have retired.

    Thus, I also use as reference ammunition, loads assembled using published data where the psi was measured with a piezo transducer and complete components for the load plus the OAL are listed. I then duplicated those loads with the same components. So far all of the duplicated loads have produced basically the same psi in my test barrels as was listed within expected +/- test to test variation.
    Last edited by Larry Gibson; 12-17-2023 at 10:16 AM.
    Larry Gibson

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  13. #13
    Boolit Grand Master

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    No disagreement at all Larry. If you are using reference ammunition/pressure to check and following procedures then your results should be just fine. As I said, I have no personal hands on experience with pressure trace systems.

    The point was that my friend does have experience and in that experience he has found that some people with pressure trace systems have reported pressures that in some cases differ significantly from professional pressure testing results. I see that the SAAMI recognizes two pressure testing systems: copper crusher and piezelectric transducer. They do not incluide strain gauges nor do I see lead crusher system which we know was used for black Powder and shotshells but not by SAAMI I guess.

    Is there a disagreement with the statement "...he has seen amateur results that show far different pressures than published/professional tests show."? That is not saying your results are different than professional pressure testing results, just that he has seen results posted on forums that do differ significantly from professional pressure testing results. Basically, don't believe everything you read on the interent.

    The OP was asking about LUP to PSI As you know it isn't a direct conversion because there are variables and results are not necessarily linear.

    Oddly, I do not see LUP discussed in SAAMI, though I may have missed it, but the lead and copper crusher systems operate in the same manner using deformation of the crusher as an indicator of peak pressure. There again there are variables and the pressure/deformation aren't linear so LUP and CUP units are not directly convertable to PSI.

    As for my strain hardening comment where I incorrectly called it work hardening, from:

    https://iopscience.iop.org/article/1...9/1/012048/pdf

    page 7:

    "It can be observed that the crusher material shows a much more
    pronounced strain hardening than OFHC copper, which could most likely be explained by the crusher
    material being a copper alloy (instead of the initially assumed pure copper material)."

    Also, from:

    https://www.hindawi.com/journals/ijae/2017/3616932/

    "Abstract

    Gun chamber pressure is an important parameter in proofing of ammunition to ensure safety and reliability. It can be measured using copper crushers or piezoelectric sensor. Pressure calculations in copper crusher method are based on linear plastic deformation of copper after firing. However, crusher pressure deformation at high pressures deviates from the corresponding values measured by piezoelectric pressure transducers due to strain rate dependence of copper. The nonlinear deformation rate of copper at high pressure measurements causes actual readings from copper crusher gauge to deviate from true pressure values."

    Both of which help to explain why LUP/CUP is not directly translatable to PSI.

    Longbow

  14. #14
    Boolit Grand Master


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    Longbow

    Your friend certainly has the same experiences with many postings of Pressure Trace systems measurements. In some of them, of which I was able to find out the procedures used by those who've posted results really out of sync with "professional pressure testing results", I have found the procedures left a lot to be desired, especially with the placement of the strain gauge. Most of those users simply glued the gauge on the chamber area of the test barrel. Some placed it even forward of the chamber. SAAMI specifications sho the exact location a piezo transducer is to be placed. I place the strain gauge in the same location.

    Additionally, many Pressure Trace users still try to make a comparison of their measured pressures to older C.U.P. measurements.

    If you delve into what is in the piezo transducer that makes it measure pressures you find it is, in fact a strain gauge. The difference between the two is simply what is measured. Neither measure the actual pressure of the fired cartridge inside the case. They both measure a result of the cartridge pressure pushing on something else, I.E. straining something else. That is a secondary measurement and is the way we measure many things. The piezo transducer measures the "strain" of expansion of the cartridge case on the transducer head. The strain gauge measures the "strain"/expansion of the barrel by the expanding cartridge. The software for each method then converts that "strain" measurement into psi.

    I believe that to be an assumption which may not be correct. The reason is the last time I worked with a C.U.P. test fixture the specific lot of copper [certified pure copper] pellets came with a table which converted the amount of 'crush" to pressure. There also was a certification stating the pellets of that lot had actually been pressure tested [calibrated if you will] by actually crushing them with a known pressure. If that is the case the calibration and, thus, the conversion table produced, negates the "hardening" factor.

    Shotshell pressures are generally lower than copper pellet can be crushed reliably or consistently. For measuring shotshell pressure L.U.P. system is essentially identical to the C.U.P. system. The difference is that certified lead pellets are used instead of copper pellets. The same type of certified and calibrated table which converts the amount of crush to pressure is included with each lot of lead pellets. SAAMI, at this time only measures and sets standards for shotshells using a piezo transducer.
    Last edited by Larry Gibson; 12-17-2023 at 05:27 PM.
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  15. #15
    Boolit Grand Master

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    On the LUP/CUP topic, I am not finding much on lead crusher testing. Do you know if it was "old SAAMI"? LUP is used in many manuals but I see little information on lead crusher testing. SAAMI lists copper crusher and piezo buty no mention of lead crusher testing.

    I would expect that nowadays testing would be by piezo or strain gauge rather than the crushers anyway but I am curious since lead crusher testing must have been used for many years for low pressure applications like black powder and shotshell pressure testing.

    Longbow

  16. #16
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    https://saami.org/faqs/#lup-cup-psi-preassures

    What is the difference between LUP, CUP and PSI pressure designations?
    For many years gun chamber pressure units had been commonly referred to as “pounds per square inch”, which was not technically correct. The older method of pressure measurement involves a piston through the side of the chamber compressing a lead or copper cylinder in which the measurement of the degree of compression is indicative of the maximum relative pressure generated. With the advent of the electronic transducer, it became necessary to indicate by some means the method and equipment used to determine the pressure values given. This is important, since the pressure values determined by one method cannot be mathematically converted to values for another, despite claims to the contrary. Likewise, the limiting pressure values for the different systems are not interchangeable.

    SAAMI created the designations of “Lead Units of Pressure” (abbreviated LUP) and “Copper Units of Pressure” (abbreviated CUP) to clearly indicate the system used in determining pressure results and/or limits. These designations apply only to values with the particular crushers, test gages and methods as outlined in SAAMI technical procedures. The terms LUP and CUP represented a change in name only. The pressure testing equipment, techniques and the numbers themselves are essentially the same as those associated with pressure units expressed as so many “pounds per square inch” prior to the advent of the piezoelectric transducer method. The term “psi” (pounds per square inch) is now reserved for electronic (piezoelectric) methods of measuring pressure, which is the predominant system in use today.

    By convention, units of pressure are reduced by a factor of 100 when put in tabular form. For example, 100 LUP is actually 10,000 LUP. 480 CUP is actually 48,000 CUP and 220 psi is actually 22,000 psi.


    https://saami.org/glossary/lup-lead-units-of-pressure/
    LUP (LEAD UNITS OF PRESSURE)
    (Obsolete) A pressure value determined by means of lead crusher cylinders.
    2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."

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  17. #17
    Boolit Grand Master

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    There we go! Thanks for that M-Tecs!

    I was looking in the wrong place for LUP. The current SAAMI specs mention copper crushers and piezo but no lead crushers. i didn't dig deep enough.

    Longbow

  18. #18
    Boolit Mold
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    Some of the older calibers have not been updated to piezoelectric standards i.e. had new protocol testing procedures established that conform to modern testing techniques. Consequently the old CUP protocol still applies to them. But there are not hundreds of shotgun gauges to update so SAAMI updated all of them when piezo testing came into vogue.
    One other point about PT II and other strain gauge consumer grade systems. Their software does not, to my knowledge, adjust the pressure readings in a progressive fashion. That is to say as I work my rifle loads I correct for a specific pressure. In 300 WM and 375 Ruger my "Reference Standard" loads run right at 60kpsi. When entering the correction factor into the program it adjusts the reading only at that pressure and not at lower pressures. If you have a 10kpsi adjustment (very real numbers) it will show 10kpsi adjustment across the board. If the strain gauge is reading 30kpsi the program will adjust it to 40kpsi. I suppose that if it could read a pressure of 8kpsi it would output 18kpsi. So when adding a correction factor in the software it is accurate only at that specific pressure. Thus in 300WM and 375 Ruger I assume it is correct only at my personal max chamber pressure of 60kpsi. Hope that clears up some of the questions about how to correct a strain gauge. If you impute the barrel parameters down to the 1/10,000th of an inch (I did) you can still get readings that are 10kpsi or more off. Even how well the strain gauge is attached to the metal greatly affects the reading. So that is why you test with a known load and add the correction factor to match that load. If not you could easily be running 70kpsi or more thinking you're in the safe zone.
    In the not to distant future is a strain gauge on a shotgun barrel. The pressure is not what determines if it will work. The gauge measures barrel expansion in diameter over the chamber. On thin shotgun barrels there may be enough expansion to get usable results.

    KB

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  19. #19
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    The Oehler M43 does not have such and "input" for the correction factor to be entered into the software. The correction factor is obtained from testing "reference" ammunition used to manually, with a calculator, compute a corrected psi from the psi the software gives. I wasn't aware of such a correction capability in the Pressure II Trace system I have. I will check the manual.
    Larry Gibson

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