That crossed cannons with a '2' in the middle was a final black powder proof, one shot per barrel at 8,818 psi and was used between December 14, 1929 to July 9, 1931. The other proof mark on the flats shows that the gun was reproofed after 1931. Does that make any sense? Plus that 'F' mark takes it back to 1933, if that's just a 'F' and not an 'FA'. I can't find what 'FA' means. Some what confusing!