1907 headspace change, does anyone know why?

[Edward Horton]

The SAAMI sets civilian cartridge and the chamber standards in the United States and the SAAMI did not come into being until 1926, the Lee Enfield rifle was officially adopted in 1895.

The SAAMI deals with commercial standards and doesn't even tell the American military how to set chamber and head space standards on military rifles.

Having said that I feel confident that the civilian American SAAMI wasn't going to tell the British military what the head space and chamber standards should be on the British Enfield rifle 31 years after the Enfield came into being.

It was a British Military decision to change the head space in 1907 and NOT the American SAAMI which would not come into being for another 19 years.

I was looking for historical British answers like improvements is .303 case design and manufacture or a new rifle was in the works and the head space was increased to extend the Enfield Rifles life cycle.