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Subject Topic: Difference between CUP qand PSI Post ReplyPost New Topic
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TallTexun
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Joined: March 18 2005
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Posted: April 01 2005 at 11:26am | IP Logged Quote TallTexun

Hey!

Whats the difference between CUP and PSI in pressure data,

What is CUP.

thanks

bob
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Rod WMG
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Joined: July 10 2003
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Posted: April 01 2005 at 12:03pm | IP Logged Quote Rod WMG

TT, this is a recurring topic. There is a lot of confusion over this.

There is no direct correlation between the two, though both measure pressure. They measure it in different ways. "Copper units of pressure" (CUP) involve actually crushing copper with a hole drilled in the chamber of a test gun. PSI is a measurement taken electronically as I understand things.

Although the figures may be very close for some rounds with the same loads, they aren't the same and, contrary to some statements, there is no conversion from one to another.

The industry seems to be moving to PSI exclusively.

Hope that helps.
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rhead
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Joined: August 27 2003
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Posted: April 01 2005 at 7:01pm | IP Logged Quote rhead

CUP has a time element in it, which makes a direct correlation between CUP and PSI very vague. CUP is an indicator of the area under the curve where the pressure was greater than the yield strength of the copper crusher pellet.Think in terms of time spent above a fixed pressure and how much above that pressure. If the pressure is too low a lead crusher pellet is used. PSI is the peak pressure reached when firing. So the difference would also be correlated to the powder charge and the bullet weightalso. In theory as the powder burn rate increases or the bore size increases ( to get a quick increase and decrease for the pressure spike ) The relationship should aproach lineraity.
It is two different ways of measuring two different things. PSI would probably do a better job of predicting an explosive failure and CUP a better job of predicting stretching and loosening.
Too much of either is of course bad.
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TallTexun
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Joined: March 18 2005
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Posted: April 02 2005 at 3:17pm | IP Logged Quote TallTexun

Thanks Guys!
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