I am trying to cross check the Proof load / marks for 375 Flanged magnum.

I have seen 54 gns, 56 gns (Cpt Curl's H&H Royal) and have just seen one on GI that was re proofed at 60 gns / 300.

Can anyone clarify for me or check to see what
any guns they have are stamped ?

While we are at it, what was the proof for the 375 2 1/2 " ?

I've got 40 gns - 320 Max ?