Are you sure it was a Mannlicher
Schoenauer or was it an earlier model of Mannlicher?
You may be describing a cartridge developed in 1905 by Holland and Holland which went by several names including .375/400 Holland & Holland, .375 Belted Nitro Express, and .375 Velopex. It was the first 'belted' cartridge and was 3.0 inches in overall length with a case length of 2.5 inch.
Though some Mannlicher sporting arms were set up for the cartridge, I have never heard of a Mannlicher
Schoenauer chambered for such.
The
Schoenauer of Mannlicher Schoenauer refers to the wonderful Schoenauer rotary magazine which, until 1924, did not accept cartridges beyond 2.95" in overall length.
The Model 1910 Mannlicher Schoenauer was chambered for the 9.5X57 MS (.375 Nitro Express 2.25") which was _not_ a belted cartridge and was designed to compete with / replace the Velopex. To my knowledge, _all_ Mannlicher Schoenauer rifles and carbines of Models M1900 through M1910 (as built) accepted only their specified cartridges, all of which were rimless and _none_ of which were belted.
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