I have an empty red and yellow box of Kynoch .32-20 cartridges with the date stamp 10 L I which must be 10th May 1960. The box clearly states

"These cartridges are fitted with NON-RUSTING CAPS".
The address is stated as Imperial Chemical Industries Limited, Metals Division, Witton, Birmingham, England.

There is no postal number for the district of Birmingham, let alone a post code (aka Zip Code for the cousins).