Today I bought this case, which is for the British QF 6" Mark 5 Naval gun of the 1950s. This round is, as far as I know, the largest cased round ever used in British service. It was a separately loaded design.
My case was made at ROF Birtley, Newcastle-Upon-Tyne in 1959.
There is some more information on the gun here:
Rick should know this: Didn’t Chuck Norris have a handgun chambered in this calibre?