850 kg/cm2 proof was commonly used for entry level Basque 12/70 guns of the 50's through the early 70's. Better grades carried 900 or 1000 kg/cm2 proof with some 12/70 pigeon guns 1200 kg/cm2.
Kg/cm2 as determined by lead crushers is a different measure of pressure than BAR as determined by modern piezo transducers.
BAR was used only after the CIP standards were adopted about 1970
70 mm = 2 3/4"
850 kg/cm2 proof = 12,090 psi for a service pressure of 566.6 kg/cm2 or 8060 psi BUT as measured by lead crushers, so by modern piezo transducers the pressure would be + 10 - 14% or about 9000 psi
900 kg/cm2 proof = 12,801 for a 600 kg/cm2 = 8534 psi service pressure + 10 – 14% or about 9500 psi
1000 kg/cm2 proof = 14,223 psi for a service load of 9,473 psi + 10 – 14% or about 10,500 psi
1100 kg/cm2 proof = 15,645 psi for a service load of 10,430 psi + 10 - 14% or about 11,500 psi
1200 kg/cm2 proof = 17,068 psi for a service load of 800 kg/cm2 = 11,380 + 10 – 14% or about 12,500 psi
