Broke out the loading manual and the education continues! 6.5x54 Mannlicher-Schoenauer fits perfectly the dimensions of the fired 6.5 Carcano Prvi Partisan cases. So!

The barrel stub DOES read "6.5MM". The folks doing the conversion just didn't specify WHICH ding-dang 6.5 mm cartridge.

There's a lesson to be learned here. Will I absorb it? Eh, probably not... Y'all feel free to laugh at me, though!