Burrard reported in 1955 that the "Highest Mean Service Pressure" of 4 Tons was 12,320 psi = 850 BAR
The standard 10g 2 7/8” load was 1 7/16 oz. 4 Dr. Eq. at a standard service of 9,296 psi and max. service 11,984 psi
He didn't report the 3 1/2" standard