No, it is not.

The thread is titled 8mm. Does "*mm" of your post also indicate 8mm?

Casper is absolutely correct regarding chamber cast. When in doubt it is always the wise / safe way to go.

That said, if original and unaltered an M1908 Mannlicher Schoenauer will be 8X56 MS, one of the four Mannlicher Schoenauer proprietary cartridges.

Here is an image of original, unaltered M1908 receiver from above:

There were also, however, 8X60 MS rifles and carbines in the pre WW2 period which would be stamped 8X60 in the same location as the 'M1908' in image above.

1939 Stoeger:

The 'magazine floor plate' is also the magazine release. Press a wood dowel, bullet tip, or such into one of the holes in plate and twist plate 90 degrees, pull Schoenauer magazine down and out. The magazine may be disassembled without tools.

Schoenauer magazine: