nice catch

I am sorry to say but the chance is high that this 9,3x57R is the 9,3x57R 360 and not the .360 BPE 2,25". what is the difference? on the first view nothing, but, the german versions of the express cartridges follow the form of the original coiled cases more closely than later britisch made cartridges and chambers.
what could be the problem for you?

the coiled case have a chamber with a bigger base than becoming thinner and relativ cylindrical

https://old.municion.org/360/360CoiledBPE2_25.htm

the drawn case is conical and so the chamber is

https://old.municion.org/360/360Drawn.htm

it could be your chamber is not conical but have such a, invisible step. so a case sized with a cylindrical die will not fit into the chamber. its very little but you can't load the cartridge than into the chamber.