From the link you gave
US Army 7.62x51 chamber pressures:
Maximum: 50,000 psi
Proof pressure: 67,500 psi
This is were the problem starts in understanding the difference between 7.62x51 and 308. right numbers, wrong units of pressure. The 50,000 is the correct number but the wrong units are used, it should read 50,000 cup (Copper Units of Pressure). The crush copper method was use when 7.62x51 was pressure tested and people keep changing cup to psi and then scream that 308 at 62,000 psi will blow your 7.62x51 gun. If tested the same way and using the same units of pressure they are both the same pressure.