Pressure in loading manuals

Discussion in 'Handloading and Reloading' started by Jesse Heywood, Feb 19, 2010.

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  1. Jesse Heywood

    Jesse Heywood Member

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    I am not looking for a war over PSI versus CUP. I know the differences, and am aware that this is a hot topic.

    I have read that at one time many writers used the numbers interchangeably, which was not a good practice.

    How do you know which data is properly labeled? Are today's manuals better with this than those from the earlier versions?
     
  2. Scrapperz

    Scrapperz Member

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    You may want to read this to help better understand the 2 pressure standards.

    Read>>>>>>>PSI vs. CUP
     
  3. rcmodel

    rcmodel Member in memoriam

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    Depends on what manuals you look at.
    If anything, it is way better today then it ever was, due to affordable and accurate electronic pressure testing (PSI) equipment..

    Alliant used to publish pressure in clearly labeled format. Now, after the ATK take-over they don't, and publish the same velocity data published by thier sister company Speer.

    Speer has for many years said what the SAAMI pressure for the caliber was, and said none of the loads exceeded it.

    Hornady never has published pressure at all, just velocity.

    With Hodgdon, you may even see a mixture of the two methods as new powders are added to the line and they add more PSI tested data to previous CUP data for the caliber.

    Lyman has long published CUP pressure in older manuals, and is now using PSI in the newer calibers and CUP in older ones.

    rc
     
  4. TonyAngel

    TonyAngel Member

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    I use a lot of Accurate powder and have noticed that older data is published referencing CUP pressure measurements. The more recent data shows pressure in PSI. I guess PSI is the way to go these days. I would suspect that the PSI system is inherently more accurate than the CUP system.
     
  5. R.W.Dale

    R.W.Dale Member

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    I once had it described to me that PSI is a science and CUP is more of an art with the outcome depending heavily on the the technicians.

    Just look at the way that a certain CUP reading for one cartridge isn't necessarily the same amount of pressure as a another cartridge with the same value.

    I'm eagerly awaiting the CUP system to get tossed on the rubbish heap of history with the league, cubit, candlepower and stone
     
  6. nhm16

    nhm16 Member

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    Don't hate on the furlongs per fortnight :neener:

    Anyways anyone have a pointer to an introductory resource on DIY pressure measurement?
     
  7. Scrapperz

    Scrapperz Member

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    Try this LOL

    07141809000?hei=248&wid=248&op_sharpen=1&resMode=sharp&op_usm=0.9,0.jpg
     
  8. ranger335v

    ranger335v Member

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    Someone's pressure washer has lost a gauge.

    PSI vs. CUP is only a burning issue to those who can't seem to accept there is really no effective difference in the working information they provide. They are different and cannot be interpolated but each is accurate enough for the purpose they serve.

    PSI is the current choice for two reasons; it's faster and requires less operator precision in its use. Meaning, it's cheaper to do.
     
  9. Offfhand

    Offfhand Member

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    Post from above:

    "PSI is the current choice for two reasons; it's faster and requires less operator precision in its use. Meaning, it's cheaper to do."

    Interesting comment, have you checked prices on the current systems?
     
  10. RandyP

    RandyP Member

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    To the OP, without some means to actually measure pressure myself, and since I don't own a chronograph either, I rely on creating loads by simply using the low-med range of the data tables.

    I shoot only modern firearms which presumably have been manufactured to SAAMI specs?I honestly don't know what I'd do with accurate pressure data in the first place? lol
     
  11. 1SOW

    1SOW Member

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    I use the "the given pressure findings" to help develop my loads without exceeding the safe "range" of pressure data supplied by the company.

    To be honest, I'm only loading light to barely mid-range handgun loads, so I'm avoiding any critical need to be exact. I don't push the envelope.

    If I did load to upper limits, I would look for the latest published data from suppliers who are recognized and respected and very conservatively work up to their findings watching for signs of overpressure.
     
  12. R.W.Dale

    R.W.Dale Member

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    If cup and psi show the same things you should have no problem making a bolt thrust calculation for me using cup.

    For everyone outside the ballistics lab cup is a completely useless measurement system that's only use is representing the max pressure FOR THAT PARTICULAR cartridge.

    Take 22-250 and 280rem as a prime example

    Both cartridge are SAAMI rated for 62,000psi
    but 22-250 is rated for 53,000 cup
    and 280 at 50,000 respectively

    or better yet .223 rem vs 270win
    Both are rated for 52,000cup
    .223's PSI rating is 55,000
    vs
    65,000 PSI for 270win

    [​IMG]
     
    Last edited: Feb 20, 2010
  13. ArchAngelCD

    ArchAngelCD Member

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    krochus,
    Thanks for that table, it's the first time I've ever seen one. What is the source?
     
  14. hoptob

    hoptob Member

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    Not to steer a controversy, but why is it important to translate CUP's into PSI's? Suppose we were to find out that some 19,300 CUP load is also 21,600 SAAMI PSI load and 22,700 CIP PSI load. How would we use this information?

    Mike
     
  15. 243winxb

    243winxb Member

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  16. NCsmitty

    NCsmitty Member

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    This illustrates that developing loads in your rifle or handgun is dependent on manuals and internet data from trusted sites, and have to be treated as guides only, and not etched in stone.
    The more data that you can accrue from different trusted sources, the better that you can determine Start and Max loads for your firearm. You can never have too much data. There is often a wide discrepancy in different sources of data as to start and max loads and the given pressures indicated. There are many reasons for this, and it can be from different components used, to the test fixture or firearm used in determining min and max loads.
    When you add your firearm to the equation, you have to determine when you have reached the pinnacle for accuracy with acceptable velocity and pressure. Usually, accuracy is found somewhere in the middle of min and max data.
    You can do that by adhering to the data listed and observing your fired brass and being aware of your firearms bolt lift and brass extraction. This is a learned technique that comes with experience.
    Always err on the side of caution, and remember that reloading can be dangerous on the shooting side, if you do not follow proper procedures.




    NCsmitty
     
  17. 243winxb

    243winxb Member

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    For me, Lee has a PSI BHN chart for cast bullets. The loads i was looking at were in CUP. If i could convert cup to psi, it might be helpfull so as not to lead the barrel.
     
  18. rfwobbly

    rfwobbly Member

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    No pun intended :neener:
     
  19. GP100man

    GP100man Member

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    Post #3

    i agree with this 100% as electronics such as the piezoelectric sensors evolve so does there abilitys & that means goin to new places , inside of chambers of fire arms & even inside of the chambers of pile drivers!!!
     
  20. 1SOW

    1SOW Member

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    Heh rf:
     
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