Possible to modify a replica MP40 to fire bbs?

Hi,

I had liked to have an MP40 that is functional and can fire .177 steel bbs (not airsoft). I don't want any plastic version so it should be as accurate to the original as possible. I can't find any bb MP40 versions so I wonder if it might be possible to modify an replica version instead. It would also be a fun project to do.

I have the KWC (Cybergun) UZI steel bb version and since it's a very simple design that is also realistic with recoil, bolt and everything, my idea was if it would be possible to take the parts from a KWC UZI and put into a MP40 replica (The bolt action on a real UZI and real MP40 are very similiar so it would be rather accurate).
I would of course need to make some additional parts to make it work and modify the existing ones but that's not a problem.

The question is, what is the best MP40 replica that can be found today? Since it will be modified I don't need one with working internal parts. It's best if it's just a hollow shell. I saw the one from Denix but can't find so much info on how it's constructed. Is it hollow and what about the barell? Is it also a hollow tube or a solid piece of metal?

The most difficult part in that conversion would be the magazine. The UZI magazine must more or less fit exactly like the MP40 one since it contains the ammo, CO2 cartridge and valve.
I had liked to find some info on the outer dimensions of the Denix magazine to see if it is possible.

Maybe this would be a impossible project but if it wouldn't be to hard. It had been fun.