Shel isn't hard, not when your improvising. We're not doing a realisticly-cast plastic shell, we're just gonna assemble the barel and other components, cut a stock/foregrip out of wood, and securing the barrel in a length of plastic tubing. Simple, clean... maybe not stury. We'll see how it works. We don't need it to be fancy, we need it to work. We'll work on fancy later.
EDIT
Remember when I said think of an M14 look? when you have access to cheap lumber and carpentry tools it becomes very easy to make a gun with real wood in it. We'll need very little in the area of plastic components. The Mech box is the hard part, and I'm sure we can improve. I'm good at that.
