The reason people wanted the M40 back(me included) was because of how it felt to use, and how fun it was to use. Considering MW2's engine(IW 4.0) is different to CoD4's game engine(Quake 3.0 remake) the M40 simply IMO wouldn't work in MW2.
If you really miss the M40 that much I think you should just go back to CoD4, like me. It's a better all-round game anyway(don't even try to argue that).
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