500:

The mark "Cordite 75 GR - 500 bullet" was never used by the British

Under the 1887 rules, this mark on a .470 would read: "75 GRS - 500 GRS BULLET Max'm"; or "Cordite 75GRS - BULLET 500 GRS Max'm. Birmingham sometimes used "BALL" instead of BULLET, and sometimes used "GR" instead of "GRS". It did vary a little, the idea being to get the information on there. The mark that is present simply isn't correct though. Moreover, this style of mark was used only during the 1887-1904 period and was NEVER used with a dedicated Nitro Proof mark. The rest of the marks present are all 1904 rule or later. In 1904 the new mark became "Cordite 75 - 500 MAX", which was used until 1955.

Crown over BP, Crown over BV, and Crown over NP were all introduced in 1904. They don't go with the 1887 style mark above.

From the 1887 rules forward, the bore mark for a .470 NE was always "470EX", never ".470". "EX" was always used for an express rifle. Note the decimal point in ".470". Neither Brit Proof House has ever used one with this mark.

The case length mark (3.25") was introduced in the 1925 rules, and was in use until 1989.

The marks on that rifle aren't even a good fake. Scroll back through the Photo Archives section and look at the Proof Marks on British rifles in the photos and compare them to this rifle. You'll see what I mean.