Pressure question...

Is there a correlation ? YES (increases in CUP --> increases in PSI)
Is there an exact formula ? NO (individual cartridges test out differently when it comes to assigning CUP vs PSI ratings)

Take a look here for best explanation and to get an understanding feel:
:https://www.shootingsoftware.com/ftp/psicuparticle2.pdf


.

Two completely different systems of measurement.
CUP places a strip of copper between the case and chamber. The thickness is then measured for compression. This yields a measurement that gives an average of the pressure, which is basically one point in time during combustion.
PSI uses modern strain gauges with computers. This allows measurement over time during combustion. Results are far more precise and yield the actual maximum pressure to be obtained.

The two methods are comparable to comparing apples and oranges. Yes, they are comparable. An apple and orange are similar in shape, but the differences are difficult to judge.
The PSI measure is far more precise, and have changed reloading. In some cases larger powder charges are allowed, but in many charges are reduced. The charges with CUP are still good to use, but the PSI is preferred.
As always, start low and work up on the powder charge.

Sorry, there is no conversion formula. The different means of testing leaves no way to convert one to the other.

MEHavey said:

Is there a correlation ? YES (increases in CUP --> increases in PSI)
Is there an exact formula ? NO (individual cartridges test out differently when it comes to assigning CUP vs PSI ratings)

Take a look here for best explanation and to get an understanding feel:
:https://www.shootingsoftware.com/ftp/psicuparticle2.pdf


.

Click to expand...

We had a very robust discussion of that paper (the author is a member here) and the subject of correlating the piezo-transducer to copper-crusher pressure measurements a few months ago and IMHO that paper is dangerously wrong. Plug 357 Mag into those formula's and see how wrong it gets. I won't repeat all the arguments here but will link to that older discussion for the OP and anyone else that wants to read the rather in depth discussion we delved into there.

https://www.thehighroad.org/index.php?threads/converting-cup-to-psi.847461/

What part of correlation/Yes was unclear ?
What part of exact formula/No was obscure ?

That the formula was 'useful' -- within its very clear-stated error bounds -- is indisputable.
That people of this day and age want exactness w/o bothering to understand what lies beneath -- is also indisputable.

there is no conversion formula.

murf