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  #1  
Old 02-05-2020, 05:50 PM
22_boomer 22_boomer is offline
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Default Is there a way to cross reference CUP to PSI?

I know they are measured differently but wondered if there was a way to get a good estimate of CUP in PSI. I was checking Hodgdon for reloading the 22 Hornet and two powders they show pressure in CUP's and another they show in PSI. I tried looking it up (google) but didn't find a real answer so thought maybe somebody here might know.

Thanks,
Charlie
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  #2  
Old 02-05-2020, 06:05 PM
Johnly Johnly is offline
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You can't really do it, but from what I've seen PSI readings are higher than CUP measurements.

John
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  #3  
Old 02-05-2020, 09:48 PM
squirrel_slayer squirrel_slayer is offline
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yeah totally different system. one is deformation of a copper plug and the other is done by pizeometric equipment.
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  #4  
Old 02-05-2020, 10:28 PM
22_boomer 22_boomer is offline
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I found a site that says there is a correlation between CUP an PSI and even has a formula to convert CUP to PSI. It takes the CUP value and multiplies it by 1.156 and then subtracts 17902.0 and gives the PSI value. It seems to work OK with high CUP values but when I use the CUP value for a max load of Lil' Gun in a 22 hornet and get 29,700 CUP and use the formula (29,700 x 1.516 = 45025.2 and subtract 17902.0 it equals 27,123.2 PSI! I don't think I've ever seen the PSI value less than the CUP for the same test point. The formula seems to work on higher CUP values. The site is here: https://www.shootingsoftware.com/ftp/psicuparticle2.pdf

The fellow that wrote the piece does some of the math on the upper part of page 5. I guess I just don't get it.
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  #5  
Old 02-06-2020, 04:08 AM
georgeld georgeld is offline
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Boomer:

Just contact Hodgdon's, they'll tell you.
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  #6  
Old 02-06-2020, 05:38 AM
17tbs 17tbs is offline
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Default No

They are not measured at the same point or in the same manner.
https://www.shootersforum.com/ballis...up-tp-psi.html
http://bulletin.accurateshooter.com/...gy-cup-vs-psi/
Mathematically it is explaned below as to why you should use P.S.I. It is a more reliable method to predict failure points (stress induced yield).

http://closefocusresearch.com/calcul...ty-gun-systems

Last edited by 17tbs; 02-06-2020 at 05:46 AM.
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  #7  
Old 02-06-2020, 12:46 PM
22_boomer 22_boomer is offline
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Quote:
Originally Posted by georgeld View Post
Boomer:

Just contact Hodgdon's, they'll tell you.
I thought about doing that. Contact the tech help and ask if they have it in PSI. Thanks for reminding me.
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  #8  
Old 02-06-2020, 05:00 PM
barretcreek barretcreek is offline
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I've got a loading manual from the early '70s which evaluated data with piezo measurements. Every combination was graphed from starting to way over max. Pressures and velocities. As either increased the deviation narrowed and then increased. That was the desired range to start developing your ladder.
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  #9  
Old 02-06-2020, 07:09 PM
Daryl Daryl is offline
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The handloading manuals that list pressures, are slowly but surely converting over to PSI as noted above, it is a more accurate measure.
Hodgdon's Annual Manual is almost completely converted to PSI- by using new data measured in PSI, not mathematically changing the numbers.

I've read of formula which can convert, but this usually carries the caveat of the results being approximations only.

The European's also have a CIP(copper crusher) & PSI listings, but both of their measurements are obtained in different locations to the US's SAAMI #'s and due to that, are somewhat different in actual # although the same loads, if you get my drift.

http://kwk.us/pressures.html gives text as well as max. listings for most popular ctgs in both copper crusher and pezio (PSI) measurements, both for SAAMI and CIP(European).
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  #10  
Old 02-07-2020, 04:30 PM
Dean2 Dean2 is offline
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Any of the conversions are not accurate for all the reasons stated above. All in however, what you are trying to judge is max pressure that will work in your gun. If you have an old trapdoor 45-70, the max CUP rating works every bit as good as the max PSI rating for judging which loads to use. Both PSI and CUP are basically indicators, what really matters is what the individual gun tells you and for sure you never want to start close to the max recommend pressure using either system.
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