Hi. This is my firs try in competition. Interested to see how it will be. I have some idea about machingun, so i'll try. 

Little bit start. Just raw sketch.

Little bit researching

Functionally this gun could never work, unless you have some sort of mechanism to have the barrels rotate. I think the overall design is a bit too blocky. Look to breaking up the silhoutte and general shapes a bit more.