Marui 5.1 and 4.3 blow back units

[emilianoksa]

I have always believed these were interchangeable, and others have confirmed this.

 

However, on looking at the respective TM parts diagrams, I was surprised to find this does not seem to be the case. 

 

The serial number of the TM 5.1 bbu shell is H51-11

The serial number of the 4.3 bbu shell is H43-5

However the internal parts for the shell of both the 5.1 and 4.3 do have the same numbers and that should make them identical.

 

Can I really put a 5.1 bbu in a 4.3 slide?