Psi vs cup pressure?

psi..pressure/square inch. CUP...copper units of pressure I think Pressure measured by compression of a copper plug in a test chamber. Guess one could google it and get a conversion.
 
There is no true conversion. Each should be used on it's own.

CUP has been used for over 100 years, maybe longer. When piezoelectroic transducers were invented, we switched to that system and used PSI.
 
The pressure is measured at different places on the case, and this varies by caliber. One system might take the presure reading at the neck, wheras the other take sit in the middle of the case. Identical pressures will give differnt readings.

Mathematical formula convertion is not possible.
 
If you can find one, the speer manual 14 has a big article discussing both, and the changeover between. Some of the more modern rounds never even had a CUP rating, .40s&w is one, that never did. 10MM came out right as they were doing the first changeovers, made for interesting times with a brand new cartridge. Also mentions how CUP was good, in that PSI sometimes is a little too exact. Pressures which spike for inconsequential periods of time, would exceed PSI limits, but be perfectly safe.
 
Physics says there has to be a conversion. But CUP measurements wereso uneven that it was very hard to do.The margin of error was so great so as to say it's couldn't be done.An expert said "CUP is dead,let it rest in peace." He also said any measurement in CUP was suspect.
 
foffe1 said:
What is the difference between pressure in psi and cup?
Click to expand...

Simple. CUP is measured with a crusher gauge and is long since obsolete, while PSI can be measured with a transducer, which is merely obsolescent, or with a strain gauge, which is actually fairly modern.

Hopefully the shooting industry will soon step into the latter portion of the 20th century and start measuring pressure in MPa or Bars.
 
I think I've got psi figured out after a lifetime of C.U.P. and L.U.P., oh yea, there's BHN and BTU's in casting, grains,grams, and drams....let me be in peace.
 
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