I'm no expert but those are Birmingham proof marks, rules of 1904. Which puts the manufacture between 1904 and 1925.

Crown over BP: Birmingham Proof
Crown over BV: Birmingham View (visual inspection)
Crown over NP: Birmingham Nitro Proofed
450 EX: Caliber and "Express Rifle"
Cordite 70 - 480: Maximum bullet weight over the standard powder load (both in grains) ( beleive that this indicates that that it was proofed for semi-smokeless powder)

If anyone would car to correct me, please feel free.

-Stev