The 9.3x64 was never offered from factory in a Mannlicher Schoenauer under normal production. The latter made guns with the plastic removable magazine such as Model M and L etc. were. Several of the cartridges listed above were only offered in those later guns such as 375 H&H and 376 Steyr. If the gun in question is really a 9.3x64 than it was either a special order made by Steyr or a custom conversion. The fact that Mannlicher Schoenauer's had an action body and a rotary follower made specifically to suit the cartridge being used indicates that it is probably a conversion as Steyr would most likely not have made a new special action for a one off.

Kuduae will probably be able to shed more light on the matter.

Waidmannsheil.