From what i understand they are considered a destructive device in either semi or full auto format. Something to do with how easy it is to convert to full auto. Another one of those irrational batfe rulings.
I could be wrong though. The one i saw for sale last year needed a batfe tax stamp and was semi auto.
The saiga12 works better, its lighter better capacity and can use drum or magazine, and no federal headache
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." — L. Neil Smith