We have just a few very rare 1936-1937 ZGB33 Trials .303 magazines, manufactured at the Brno Factory in Czechoslovakia for the British Government Bren Gun contract of 1935 after extensive troop trails.
It was the vz/30 that adopted the .303 British cartridge as the "ZGB vz/30" prototype of 1930 and underwent trials from 1931 to 1932. The following ZGB vz/33 development of 1933 became the official basis for the finalized British design.
The British soon adopted the Czech Light machine gun system for the British Army in 1933 then the Brno Factory was tasked with the design work which continued well into 1935.
A number of ZGB33 .303 Test trials light machine guns were shipped from the Brno Factory in Czechoslovakia to the British Government factory at Enfield Lock for evaluation and testing in 1936-1937.