CUP and PSI

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CUP and PSI

Post by Kelsey Cooter » 02 Aug 2019, 6:04 am

So I was comparing pistol powder loads last night and decided to look into a conversion between cup and psi. And discovered they can't be converted. At least thats what I think I was reading.

What is cup and what is the point of it? Why does the adi book use both
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Re: CUP and PSI

Post by bladeracer » 02 Aug 2019, 6:34 am

Kelsey Cooter wrote:So I was comparing pistol powder loads last night and decided to look into a conversion between cup and psi. And discovered they can't be converted. At least thats what I think I was reading.

What is cup and what is the point of it? Why does the adi book use both


They are measured two different ways. CUP is a measurement of the compression of a copper slug in the wall of the chamber, PSI is a direct measure of chamber pressure.

Manuals will list pressure in the units it was measured in.
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Re: CUP and PSI

Post by straightshooter » 02 Aug 2019, 7:21 am

As stated earlier CUP is an inferred pressure reading based on the compression of a standard copper slug.
Chamber pressure expressed in PSI is usually measured more directly using piezo or high slew rate strain gauge sensors.
Piezo comes closer to reporting a true pressure curve with a more faithful indication of peak pressure rather than a pressure vs time indication but it is still insufficiently reliable in indicating instantaneous pressure excursions that exceed it's response time.
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