Eley made 7x57 ammo during WW I for two uses: The Royal Navy’s small complement of Chilean M1912 Steyr Rifles ( removed from the Chilean Cruisers being Built before WWI, and inducted into the RN…The Rifles were then used for " Mine Sinking" ( NOT “Mine destruction”) by Minesweepers in the North Sea and the Channel. The ammo was supplied in ten round Packets with the additional stamping " For Chilean Mauser Rifles" on the “Normal” British Gov’t Wrapping.
The second use was for the Serbian Army in the enclave of Salonika, in Greece, from 1914-1917; There are also various references (Public Records Offices) to British Acceptance/Inspection teams visiting Chile, Brazil, etc., buying up both 7mm ammo and Surplus Mauser Rifles (Both M93 and M98 styles) for supply to Serbia, and also 7,65 cal. Rifles and ammo for supply to Belgian Troops.
The Dummy rounds would have been made from Factory Components, and the Holes drilled by hand…the rough edges show this. ( Not “screw Mounting”). Probably made up in the RN Depot workshops from Live ammo, deactivation of Primers by use of a solvent or salt water, etc, or Heat…Primer Crimp is original Factory. Of course, they could be from salesman’s “Display Boards”, and re-assembled into a clip.
BTW, the M1912 Steyr Rifles were “Sold to the Trade” in 1919-20, having been replaced on the Two Cruisers eventually returned to Chile by 1920, with Canadian Ross Mark III Rifles, (1916 make, “LC” marked); Rifles and Matching bayonets sold off by Chile in 1970s, all “D.A xxx” marked (Directorado de Armada…Naval Directorate).