I'm sure that all the Nakata MP40s are Zinc.
There's no way I'm aware of that Zinc alloy models can be converted safely to fire Blank rounds.
The MGC MP40 which has steel recievers needs extensive strengthening work as well as new steel components to make safe for Blanks.
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Cerwyn
Hobby collector of Replica model guns and Militaria.
also member of Living History Reenactment Groups.