In short:
If the game will have the category "sub machine gun," and the game already have a standard weapon in that category (like "Sportcar" is the standard car "Island"), just create a weapon of that category (such as G-36 ) in 3D.
G-36:

Accordingly, the arms will have a different aesthetic, but will have the default behavior for the category of weapon (as in an environment TrackMania a Ferrari and a Volkswagen Beetle has the same behavior).
This is my idea. It may not be the same idea of the staff of Nadeo.
I am sorry for my English.