cup to psi ??

[GP100man]

is there a conversion chart to covert cup to psi???

:castmine:

GP100man

[monadnock#5]

The Lyman 48th doesn't have a chart, but it does list a few rifle loads for PSI. If you're looking for something specific, you might get lucky.

Ken

[Scrounger]

It's not a linear conversion so there is no magic number you can use, each cartridge is different. The .30-06 for instance is 50,000 CUP and 60,000 PSI, but the .270, if I remember correctly, is 52,000 CUP and 65,000 PSI. You have to find the SAAMI spec on each caliber. Here's a link to a list; 'crusher' column is CUP, 'piezzo' is PSI.
http://kwk.us/pressures.html

[buck1]

Lyman 47 has something if I recall..........Buck

[joeb33050]

This is from the book, 6.1
The Lyman 47th Handbook has a table of CUP and psi values for a series of cartridges (pg. 93) and says (pg. 92) "It (the table) clearly points out that it would be an error to assume any correlation between the two test methods."
However, I found this on the Internet:

http://www.steyrscout.org/intballi.htm
"New statistical data analysis suggests that for most cartridges ANSI/SAAMI Maximum Average Piezo (PSI) and Maximum Average copper crusher (CUP) taken in a "standard" barrel can be related by the following formula which has an R^2 value (a statistical measurement of certainty) of .927.
(1.51586 * CUP) - 17902.0 = PSI
While the relationship is generally within Kpsi (it assumes that the CUP was determined using ANSI/ SAAMI standards) one should not rely on this conversion for absolute maximum loads."

The Lyman 47th Handbook table, pg. 93, shows both CUP and psi pressures for a set of cartridges. This table was developed by the Hercules Powder Co.
I applied the formula to the CUP pressures in the Lyman table and the formula worked pretty well.
The left three columns in this table duplicate the Lyman table.
"ESTIMATED PSI" shows the pressure estimated using the formula above, from the CUP values in the Lyman table.
"ESTIMATED PSI/MEASURED PSI" shows percentage values indicating how close the estimated pressure is to the measured pressure.
The largest percentage is 110.77% (estimated pressure was 110.77% of measured pressure), the smallest percentage was 87.65%, and average was 100.5%.
Given the fuzziness of chamber pressure measurements this appears to be a reasonably accurate method of converting CUP to PSI and the reverse.
Heed the warning on the Internet cite-"one should not rely on this conversion for absolute maximum loads."



MEASURED MEASURED ESTIMATED ESTIMATED PSI/
CUP PSI PSI MEASURED PSI
22-250 Rem 53000 62000 62439 100.71%
222 Rem 46000 50000 51828 103.66%
223 Rem 52000 55000 60923 110.77%
6MM Rem 52000 65000 60923 93.73%
243 Win 52000 60000 60923 101.54%
25-06 Rem 53000 63000 62439 99.11%
257 Roberts 45000 54000 50312 93.17%
257 Roberts +P 50000 58000 57891 99.81%
270 Win 52000 65000 60923 93.73%
7MM-08 Rem 52000 57500 60923 105.95%
7X57 Mauser 46000 51000 51828 101.62%
7MM Rem Mag 52000 61000 60923 99.87%
280 Rem 50000 60000 57891 96.49%
30 Carbine 40000 40000 42732 106.83%
30-06 Spr. 50000 60000 57891 96.49%
30-30 Win 38000 42000 39701 94.53%
300 Savage 46000 47000 51828 110.27%
300 Win Mag 54000 64000 63954 99.93%
303 British 45000 49000 50312 102.68%
308 Win 52000 60000 60923 101.54%
8X57 Mauser 37000 35000 38185 109.10%
8MM Rem Mag 54000 65000 63954 98.39%
338 Win Mag 54000 64000 63954 99.93%
35 Rem 35000 33500 35153 104.93%
45-70 Gov't. 28000 28000 24542 87.65%

Of course the table didn't come out properly, see the book for the table.
joe brennan

[bruce drake]

http://www.reloadbench.com/gloss/cuppsi.html