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Old 11-11-2010, 08:03   #1
steve4102
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Interpreting Load Manual Pressure Data?

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
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Old 11-11-2010, 08:20   #2
Zombie Steve
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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.
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Old 11-11-2010, 09:32   #3
dudel
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Quote:
Originally Posted by steve4102 View Post
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
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.
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Old 11-11-2010, 10:21   #4
steve4102
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Quote:
Originally Posted by dudel View Post
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.

Duno, It is Hodgdon online data and it does not list test firearm.
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Old 11-11-2010, 10:49   #5
dudel
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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
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Old 11-12-2010, 05:26   #6
sourdough44
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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.
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