PleaseNote: The 8x51Rmm is the same as the older 8x50R Lebel rifle cartridges, just a new *C.I.P.
designation to correct to the real 51 mm case length. 

2 cartridges not a box. 2 different head-stamps: 8x50R and 8x51R Lebel

History of the 8x50Rmm Lebel Rifle Cartridge:

 The 8x50Rmm lebel rifle cartridges  was introduced in 1886 for the Lebel bolt action rifle and  was the first small bore cartridge using smokeless powder by a world power.

It was used by the French until the advent of the 7.5x54mm MAS cartridge and bolt-action rifle in 1932. Cartridge production ended in France in the late 1940s. and Remington also produced rifles and ammunition for the French government.

Around 2017 the *C.I.P. changed the cartridge designation to 8x51R. 

*C.I.P. is short for (The Commission internationale permanente pour l'épreuve des armes à feu portatives) or in English (Permanent International Commission for the Proof of Small Arms).