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Rifles, Reloading, Optics, Equipment
Reloading
CUPs compaired to PSIs
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<blockquote data-quote="MagnumManiac" data-source="post: 1216957" data-attributes="member: 10755"><p>J E, I know this can be perplexing, not knowing the conversion between CUP & PSI, but, I would also like to throw in another curve ball.</p><p>Depending on WHERE you place the piezo crystal also changes the PSI given.</p><p>I have a pressure trace, I use it to work up loads in absolute numbers, no fudge factors, no calibration, just raw data. Then I load 10 and take an average.</p><p>I read that CIP take their measurements from the case mouth, while SAAMI take there's from a mid point along the case. I have tried both points, and yes, the measurements are vastly different.</p><p>I have not tried NATO testing because I cannot find a definitive description of what exactly they do.</p><p>I know they test back thrust with an oiled case, but, chamber pressures are not clearly defined as to their method.</p><p>The readings at the case mouth are higher, as indicated by CIP readings.</p><p></p><p>Getting back to the original question, I recall reading that 50, 000 CUP was roughly 60, 000 PSI.</p><p>I also remember reading that CUP was so unreliable that no 2 tests ever gave the same readings, even in the same test barrel.</p><p>Why do you want to know the pressure?</p><p>It never is the same as the test barrel anyway, have proven this many times now, same charge weight, same bullet, same case, same primer, different velocity to book and different pressure. Also, most brands of brass don't show ejector marks until 70, 000psi is reached or exceeded. Some primer lots have flattened at 55, 000psi, a full 10, 000psi below max pressure.</p><p></p><p>Cheers.</p><p>gun)</p></blockquote><p></p>
[QUOTE="MagnumManiac, post: 1216957, member: 10755"] J E, I know this can be perplexing, not knowing the conversion between CUP & PSI, but, I would also like to throw in another curve ball. Depending on WHERE you place the piezo crystal also changes the PSI given. I have a pressure trace, I use it to work up loads in absolute numbers, no fudge factors, no calibration, just raw data. Then I load 10 and take an average. I read that CIP take their measurements from the case mouth, while SAAMI take there's from a mid point along the case. I have tried both points, and yes, the measurements are vastly different. I have not tried NATO testing because I cannot find a definitive description of what exactly they do. I know they test back thrust with an oiled case, but, chamber pressures are not clearly defined as to their method. The readings at the case mouth are higher, as indicated by CIP readings. Getting back to the original question, I recall reading that 50, 000 CUP was roughly 60, 000 PSI. I also remember reading that CUP was so unreliable that no 2 tests ever gave the same readings, even in the same test barrel. Why do you want to know the pressure? It never is the same as the test barrel anyway, have proven this many times now, same charge weight, same bullet, same case, same primer, different velocity to book and different pressure. Also, most brands of brass don't show ejector marks until 70, 000psi is reached or exceeded. Some primer lots have flattened at 55, 000psi, a full 10, 000psi below max pressure. Cheers. gun) [/QUOTE]
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Reloading
CUPs compaired to PSIs
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