It looks like a futuristic concept of a Mac10, the magazine would be inserted into the grip of the weapon and the ejection port could be on the opposite side we don't know, we're not the designers. What about it doesn't look "Assault" like? clearly from the silhouettes it can be broken down into several different variants for a variety of close quarters entry roles.
I'm a bit up in the air about the ammo, but hey, it's an imagined round for an imagined weapon. Looks good, I'd like to see a few more views to really flesh out all aspects of the piece.