It shouldn't matter, the MP5 is Version 2, so is the M4. The cylinders are identical, though there may be differences in the cylinder head, and there are definitely differences in the nozzle. I'm not saying that there might not be something wrong with that particular set, or even your gun's mechbox alignment.
But you're right, I have not tried this on an MP5, I was just making suggestions.
Ár skal rísa, sá er annars vill
fé eða fjör hafa. Sjaldan liggjandi úlfur
lær um getur né sofandi maður sigur.