.303 Brit "R٨L C IV"

Municion.org says it is made in 1898. How do they know this?

These were only made for a short time before being replaced by the Mark VI in 1899.

Royal Laboratory made Cordite Ball Mark IV over three financial years.

Production was:
1897/98: 162,800 rounds
1898/99: 54,504,778 rounds
1899/00: 11,131,260 rounds

Your round could have been made in any of those years.