Yep, what mangler525 said.
Either you can make it from pep, or you can make it from cardboard, wood, or even sculpting clay. I have a tutorial for how to make a Battle Rifle located
here. You can use that tutorial for a basic idea on how to make the Carbine. It goes through how to do everything from the basic shape, to detailing and adding working functions.
Hope that helps.
CHEERS!