CUPs compaired to PSIs

[J E Custom]

I still cant fine any direct comparison between the two and It would be nice to have a chart/formula
that would compare them.

I have acquired many loading manuals over the years and some have tested CUPs in pressure test barrels/gun, Most if not all load data now days is all calculated.

Some have tried and true real world loads in cartridges and barrel lengths. I still use some of them
and I would like to be able to know what PSI they were.

Reading the brass is not a very good way to work up loads and buy the time you see signs of pressure you have gone to far in most cases and with the different brands of brass comes different harnesses making it very un reliable.

Just thought I would find out if anyone could come up with a good comparison that was tested against CUPs that could give accurate comparisons to PSIs.

Here is the best information I could find and still doesn't help much. (There may not be any way to convert one to another but it would be nice to have something.

http://bulletin.accurateshooter.com...hats-the-difference-in-pressure-measurements/

Hoping some of you math prodigies could help. Any help would be appreciated.

thanks

J E CUSTOM

 

[BallisticsGuy]

This is a fraught area of discussion. Keep in mind during your readings that CIP and SAAMI testing is done slightly differently meaning CIP results are not interchangeable with SAAMI results. That also means terminology and quantities are going to vary. I won't say any of the below stuff is accurate or not but it'll acquaint you with the topic and keep me out of my flame suit.

Cliff's Notes:
These formulas produce rough approximations and shouldn't be used as a precise or accurate result. There is no way to actually cross reference the two other than doing actual cartridge side to side pressure testing.

There is also the problem of not everyone understands pressure CUP OR PSI and getting the numbers mixed up in your mind is a real risk.

USE AT YOUR OWN RISK

US Conversion (ANSI): PSI = -17,902 + 1.516 x CUP
European Conv (CIP): PSI = -2806.88 + 1.20911 x CUP

PSI TO CUP

(PSI + 17902)/1.516

CUP TO PSI
-17902+(1.516*CUP)

Further reading:
https://www.shootingsoftware.com/ftp/psicuparticle2.pdf

 

[Hugnot]

I always look at established load data, in this situation is Hodgdon's 6.5X47 Lapua data for 140 Berger VLD using max charge of 39.5 gr. StaBALL 6.5 having a CUP of 52,400. Being curious of about the approximate PSI equivalent would be I stumbled upon the link provided above. Reading into this stuff I found a regression analysis that looked valid. A formula was shown. I took the formula and plugged it into an excel spread sheet to convert both. The regression analysis sure shows a correlation between CUP & PSI.



The formula for each conversion is shown - these are ANSI CUP & ANSI PSI values.

The regression plot is shown on page 4 of the link

I have a 8 twist 6.5X47 Lapua and some 140 grain Barnes Match burners & some StaBALL 6.5 for shooting steel. I also have some 123 ELD's that I might shoot at rodents, if seen during the same trip. I will work up a load for both.