I couldn't bring up the thread on the 16g site, and some here so enjoy cut and paste drivel I thought I'd post it with apologies.
Bro. Larry did all the work.
The "Tons" mark (which is service pressure) was not used until 1954. Between 1925-54, only the chamber length was marked. 1904-1925 guns would only have the shot charge and 'Nitro Proof'.
There are three pressure measurement systems (lead crushers/LUP, copper crushers, and piezo), and two standard systems of measure units (USA/SAAMI and CIP/British/European) and different units within each system (psi, tons/sq inch, and bar in kg/cm sq).
There is essential NO formula to convert BAR expressed as LUP (CIP) to PSI (SAAMI). LUP + 1000 does not reliably predict the actual piezoelectric transducer measured pressure.
Starting in 1989, all CIP proof data was marked in metric using BAR as the unit of measurement. The use of TONS per square inch was dropped. Under this system, 850 bar represented standard proof, with 1200 bar being special or magnum.
2 1/2" chambered guns are usually proofed 850 bar.
2 3/4" chambered may be proofed 900 bar or higher.
Per the 1954 Rules of Proof, here are the approximate CIP service pressure values:
3 tons--8,938 psi
3 1/4 tons--9,682 psi
3 1/2 tons--10,427 psi
4 tons--11,917 psi
These numbers SHOULD apply to guns proved under the 1925 rules; a 2 1/2" chambered gun proof would be equivalent to 3 tons; a 2 3/4" chambered gun to 3 1/4 tons.
European (CIP) proof pressure of 850 kg per sq. cm. (BAR) = about 13,920 psi proof pressure = about 10,730 psi service pressure (SAAMI)
Last edited by Drew Hause; 10/01/13 05:40 PM.
