According to the; ‘British Small Arms Ammo,’ site the .303 MkVI production ended around 1910.
The appended images show two .303 Mk VI with a manufactured date of 1917.
On both examples the Royal Laboratory headstamps have a slightly different layout.
The neck of both cases is slightly blackened, but; it is unclear to me if this was as a result of the propellant, or intentional identification blackening.
Could a batch of Mk VI have been manufactured for older rifles, that had been pressed into wartime service?
20000 Ross MkII3* rifles purchased by the US were sighted for the .303” MkVI cartridge."
Any assistance would be much appreciated.