This particular 20mm casing was manufactured in Royal Ordnance Factory Radway Green, Radway Green, UK The “OeZ” marking means “Oerlikon, Loaded with Nitrocellulose powder”. This maring was used to differentiate the semi-rimmed Oerlikon rounds with the similar looking (but not interchangeable) 20m Hispano. In British service, a “Z” stamped on the base of a case 20mm or below in calibre indicates that the case is loaded with nitrocellulose flake powder. This is opposed to the typical British Cordite “spaghetti” rod type propellant.
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