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Interpreting Load Manual Pressure Data?

Discussion in 'Reloading' started by steve4102, Nov 11, 2010.

  1. steve4102

    steve4102

    2,308
    674
    Jan 2, 2009
    How do you interpret Max loads with different pressures? For example, Hodgdon data for the 40 S&W with 180gr XTP lists max pressure for all loads around 32-33K except for one. This exception is SR 4756 with a Max load pressure of 28,800psi.

    Why such a large difference in Max pressure? Does this mean that this powder can produce similar velocities at lower pressure or does it mean that this bullet/powder combo should be kept lower than normal cuz it has issues like getting squirrely (technical term) when loaded to SAAMI max pressures?

    Thanks
     
  2. Zombie Steve

    Zombie Steve Decap Pin Killa

    18,083
    18
    May 31, 2007
    Old Colorado City
    I interpret it as meaning if you go beyond this point, you'll see a wicked pressure spike. That extra tenth of a grain produces more pressure than it did when you were in the mid-range of the data.
     


  3. dudel

    dudel

    5,020
    550
    Dec 10, 2008
    Texas Hill Country
    Was the data collected from a test receiver or from an actual gun? Different people do it differently and end up with different results. I prefer the data that comes from actual guns and a strain guage; but sometime what you get is lab data.
     
  4. steve4102

    steve4102

    2,308
    674
    Jan 2, 2009

    Duno, It is Hodgdon online data and it does not list test firearm.
     
  5. dudel

    dudel

    5,020
    550
    Dec 10, 2008
    Texas Hill Country
    Here is a good writeup on how pressures are tested.

    http://hunting.about.com/od/ammo/f/faq_pressure.htm

    On a test receiver, you can generate actual CUP readings. On a real gun, with a strain guage, you use a formula to calculate the CUP from the reading.

    HTH
     
  6. sourdough44

    sourdough44

    3,019
    131
    Jul 23, 2007
    WI
    I cross reference several manuals to see how they compare with the charges. Of course powders behave differently, then you have bullet differences. One other thing to consider is max pressure for a given cartridge. I'm more careful messing with the top end of a higher pressure 40 s&w loading than I am loading a low pressure 45 Colt or 38 spcl. That is even more true when I will be shooting them say in a modern Ruger or 357 chambered gun. Some powders 'spike' more or faster than others. There are times when you can 'interpolate' some when reloading & other times when you shouldn't deviate from listed data.