Charger approval dates were:
Mark I List of Changes Paragraph 11753 16 Jan 1903
Mark II List of Changes Paragraph 13465 24 April 1906
Mark III List of Changes Paragraph 18973 15 Feb 1916
Mark IV List of Changes Paragraph 19786 30 Oct 1917
The Mark V charger was also from 1918 but was not finally approved due to the end of the war.
Regards
Tonye
Many thanks Tony - I wasn't wrong, nor was I entirely right! But would it be safe to say that the Mk II .303 chargers were the most commonly used ones during WW1?