DanF is dead on. I have hands-on experience with these. The stock is welded, but the one I used would be impossible to break the welds on the stock without ruining the upper. Also, the bolt is different from the full-auto version, making it impossible to convert without a parts kit that changes the upper and bolt.
Malo periculosam, libertatem quam quietam servitutem." (I prefer the tumult of liberty to the quiet of servitude.). Thomas Jefferson
"All that is necessary for the triumph of evil is that good men do nothing."
-Edmund Burke, Loosely translated from Thoughts on the Cause of Present Discontents. (1770)