If i were you i'd either go NAVY, Air Force or Army. I knew a guy in my graduating class and he was in the Marines. He was killed by a car bomb last year. But that's your choice and you will do our nation proud.
Wow that's awesome. It looks almost like a light machine gun, in which case I'd figure a larger clip (like a drum or box clip) and a bipod might be more practical. But at the same time the configurations you show make it seem more like an assault rifle, what with the foregrip, silencer and grenade launcher (I think...) So, the designation of a Heavy Assault Rifle is quite accurate, imo.
It does look like a mid thing between an assault rifle and an light machine gun. The small magazine would be detrimal though, so I'd have to agree with your assessment of adding a drum clip. Box clip might become too unwieldy when put into bullpup like that, maybe a casket magazine?