find the 1931 Manufrance catalog in the net
https://www.flickr.com/photos/taffeta/sets/72157622456911039/
while the ammo page have the 10,75x68 and the 405 Winchester for the old and the new Rival rifle there is no page showing the new Rival in 10,75 with a M 98 action in production since 1930.
this ammo is clearly loaded with a french powder also a 450 NE and a 577 NE cartridge. this ammo is unknown to cartridge collectors but maybe there was some kind of powder or ammo monopol than and they import cases and bullets and load it with french powder.