.303 Brit "C.18.F3 VII Z"

What’s the meaning of “C” and “F3”?

Government “Cartridge Factory Number 3”

Government Cartridge Factory No.3 was located at Blackpole, Worcestershire and was operated by Kings Norton Metal Co. on behalf of the British government.

It commenced in 1917 making 7.62x54mm for the Russian contract and switched to .303 inch in January 1918. It closed in March 1919 and the machinery put into mothballs. In 1940 it was activated again and became Royal Ordnance Factory Blackpole using the “BE” code.

You should read your IAA Journals. I wrote a detailed article about the GCFs in December 2008 issue.