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This is a discussion on Rookie Mistake within the Reloading forums, part of the Firearm Forum category; Yellowsevenpot, Perhaps you got copper units of pressure (CUP) confused with pounds per square inch (psi). The two are NOT the same. In virtually all ...


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Old April 30th, 2017, 09:14 AM   #16
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Yellowsevenpot, Perhaps you got copper units of pressure (CUP) confused with pounds per square inch (psi). The two are NOT the same. In virtually all handgun loads, CUP will be higher than psi, with the same powder charge. With rifle loads, it's just the opposite where psi will be higher than CUP with the same powder charge.

Another major issue is the procedure used to test pressure. The old "crusher" method is measured in CUP whereas the newer and much more accurate method is measured in psi. Although SAAMI still maintains specifications for both test methods, the crusher method has been phasing out since 1993. So .... anytime you see pressures stated in CUP, the old pressure standards were used with the crusher method.

In 1993, SAAMI changed the pressure standards for 357 Mag, 41 Mag, and 44 Mag. 357 Mag max pressure used to be 43,500 psi and is now 35,000 psi. 41 and 44 Mag used to be 43,500 psi and both are now 36,000 psi. It is not unusual to find "old" reloading data even in newer reloading data sources.

Using two different pressure standards is confusing at best and in the worst case, it could get you into a heap of trouble. Here it is 24 years after CUP became obsolete so just about all references to chamber pressure use the piezo electronic testing methods rated in psi. That way you have an apple to apple comparison instead of confusion. I would NOT trust any load data that used the old crusher method so when I see chamber pressure rated in CUP, I look for a different source.




Last edited by Iowegan; April 30th, 2017 at 09:23 AM.
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Old April 30th, 2017, 05:54 PM   #17
 
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Thank you for the info Iowegan, I didnt know the history. Both of the data sources, hogdon online database and the lyman cast bullet handbook, are measured in cup.... I am still looking into this as I find it interesting. Hopefully hogdon will get back to me.

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Last edited by Yellowsevenpot; April 30th, 2017 at 06:00 PM.
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Old May 1st, 2017, 07:04 PM   #18
 
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be safe pull them and start over.
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