@ HaloFreakX,
Actually, it feels realistic in weight with just the cardboard, even more with a barrel and Rondo on it. So, depending on what kind a cardboard you use (Thin, Thick), I would say that it would feel realistic.
Thanks everybody for the comments on the AR, but if you have the time to do this (I didn't have much time, plus I didn't have an X-acto knife, so scissors don't help with the fingers), I highly recommend it.
Sorry guys, had to run to town yesterday, so I couldn't do any work, I might get out there today.