I will have to take your word for it, but here are my comments:
The whole case is pushed through the FCD body only, basically through the carbide ring. This means that the carbide ring should have an inside diameter larger than the cartridge specs. Following are the SAAMI specs for 9mm and 9x18 Makarov.
View attachment 971521
View attachment 971522
The largest diameter for the 9mm cartridge is .394 - .010 and the largest diameter for the 9x18 MAK is .392 - .010.
You would think the carbide ring inside diameter for the 9mm should be at least .002 larger than the 9x18 MAK.