all of you should really know what you're talking about before you say anything.
it is, in fact, simple to modify a GBBR OR an AEG into a bullet firing weapon.
here it is... the DIY.
be sure to write this down ASAP, as the Man will have it removed from the web within hours:
1) buy an airsoft gun. easier with a GBBR, and an AR type weapon would be best
2) replace the gun with a real steel gun (of the same weapon type)
3) paint the flash hider orange
4) fill in any serial numbers with bondo, or other fillers.
5) paint filler black to match the rest of the weapon
6) tell everyone it is an airsoft gun converted to fire bullets.
there you go guys and girls.