Would be easier and cheaper to just get a slide fire stock. But with the jump to full auto (or worse in the case of the slide fire...bump fire), you run into a whole slew of problems. Namely reliability and expenditure of ammo. Rambo lied, full auto is not used for slaughtering rooms of people. It's for making the other guy take cover and not shoot back at your guys.
Which leads to "well what about drum magainzes"....those are not reliable. If I recall, dipshit at the theater had one and it jammed. Once you get past 30, the reliability starts to plunge.
I believe, and I admit I could be wrong here, that suppressors were regulated around the 30's because of poaching. Today there is the perception that they make a gunshot silent, they are still pretty damn loud, just not bust your ear drums loud.
edit: didnt araysar say he had a grenade launcher? I vaguely remember this lol