Can anybody add to the very limited knowledge I have regarding this rather unusual Swiss experimental cartridge? Datig refers to two versions, this rimless version being the 7.5mm Rubin M1885 and a similar but rimmed version being the 7.5mm Rubin M1886. Presumably these were forerunners of the Swiss 7.5mm Schmidt-Rubin G.P.90 but I understand they also played a part in the design of the British .303.
I’ve tried to photograph the unusal brass collar which sits in the casemouth and which, in turn, holds the bullet. The round also has a very unusual flush primer although my specimen has unfortunately been struck and misfired.
Were all of these made in Switzerland or were they possibly made in the UK as well during development of the .303?