1907 headspace change, does anyone know why?

[Alan de Enfield]

Tracking this change backwards gets original .303 headspace very close to current US SAAMI standards doesn't it? I have always suspected that current SAAMI specs are closer to the original dimensions than are current British standards.
Why? The .303 British was never a US military cartridge subjected to the British engineering changes. However it was a US commercial round subject to US industry standardization. Just because the British military needed to change did not mean there was any reason to change US commercial manufacturing practice.

So - when SAMMI was founded in 1926 (I think) they sat back and had a great debate :

"Shall we take the max headspace on a British 303 as that stated by the miltary prior to July 1907 (0.072"), or shall we take that used in July 1907 onwards, (0.074") no - lets take neither and invent our own (0.070")

0.072" is closer to 0.070" than 0.074" is, but there again, so is 0.068"