A question on proof pressure of a modern gun.

My on the barrel flats of my Wm. Douglass 470 London Proofed
in 1998, is stamped the proof pressure of 3120 BAR and I believe the gun was regulated with Federal ammo. On the top of the barrels is printed " .470 NE 500 grain bullet. What proof pressure is this, Pmax,Pmin, Pave? Is 1 BAR equal to 14.7 psi at sea level? So 3120 x 14.7 psi = 45,864 psi????

In the A-Square reloading manual "Any Shot You Want.", 470
NE is rated with a Piezo psi max ave at 39,187 and
Maximum individual at 45,065. Their recommended loads "red
line" anything over the 39,187 figure.