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Author Topic: Is there a formula to convert c.u.p. to p.s.i.?  (Read 750 times)

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Offline carpediem

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Is there a formula to convert c.u.p. to p.s.i.?
« on: November 24, 2003, 11:22:35 AM »
Does anyone knbow of a mathamatical formula to convert copper units of pressure to punds per square inch?

Kindest regards,
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Carpediem

Offline Aladin

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Re: Is there a formula to convert c.u.p. to p.s.i.?
« Reply #1 on: November 24, 2003, 11:33:06 AM »
Quote from: carpediem
Does anyone knbow of a mathamatical formula to convert copper units of pressure to punds per square inch?

Kindest regards,


Nope. I use percentages though. Say the 06 is listed as 35,000 cup in the Lie-man cast manual-- which is 70% of the max of 50,000 cup.  

70% of a psi max would be 42,000 psi-- with scale max-ing at 60,000.

Thing is-- psi's and cup's chg by caliber and industry loading levels.  The 45/70 industry standard is 28,000 psi and cup-- a caliber where the figures out work to be the same. Yet most 45/70 is downloaded to accompdate the older weaker guns.
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Aladin

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Offline richp41

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Is there a formula to convert c.u.p. to p.s
« Reply #2 on: November 24, 2003, 12:19:48 PM »
Absolutely no direct conversion. Some cartridges appear to be the same and others are quite different.  The only safe approach is to NOT assume CUP and PSI are interchangeable and convertable.
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Offline carpediem

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calculating bullet obturation using psi
« Reply #3 on: November 24, 2003, 04:10:24 PM »
Thanks for the info guys.

Is there a reloading manual that lists pressure for lead cast bullets in psi?  I have a formula to calculate bullet base obturation using psi, (as discovered in Rifle Magazine's Handloader, December 2003, No.226, Page 6; in the article written by Dave Scovill, entitled "BHN and BULLET METAL").

In a nutshell, you multiply the Brinell hardness of your lead alloy by 1,422 to give you "the pressure required to cause that particular alloy to upset under pressure in a gun."

Thanks for the help.

Kindest regards,
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Offline richp41

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Is there a formula to convert c.u.p. to p.s
« Reply #4 on: November 25, 2003, 05:08:22 AM »
The only source I have is the Lyman cast bullet handbook which shows CUP for some of the loads. If you use the published formula to calculate the yield point (obturation begins) also keep in mind that the tensile value (failure point) of the alloy will be about 30% higher. Your chamber pressure needs to be between the yield and tensile values for the bullet to work properly. Rich P
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Offline carpediem

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Is there a formula to convert c.u.p. to p.s
« Reply #5 on: November 25, 2003, 06:51:23 AM »
Thanks for the info richp41.  I was wondering at what point the bullet would fail.  

This should be an interesting experiment.  Any excuse to get to the range to do some shooting.

Kindest regards, :wink:
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