The 8 Lebel is the mother of all modern rifle ammos.
You can see that it influenced both the 303BR and the 8x57R (i.e they were copied from it)...
The strange bottle shape comes from the 11mm Gras which was the parent cartridge. The 2 follow ups replaced that shape with the .400 basic... Which does make more sense. The 8x57 is basically the 303 with the Lebel bullet...
WC-