I've been finding references to the following rounds being chambered in the M-S rifle:

7x54mm Mannlicher-Schonauer
7.63x54mm Greek Mannlicher-Schonauer

Outside of them just having a mention, I've not been able to locate any specific information on them.

Does anyone have any information on them? When and in what rifles were they used in? What are the cartridge dimensions? Were these experimental calibres that never caught on?