A gay Radical Islamic Fundamentalist walks into a gun show......
Gadahn "the American" who is so gay that he signed up with al Qaeda for the chance to live in a cave in Afghanistan with a bunch of sweaty men has been reading the Brady Campaign(or whatever they are calling themselves this month) website and has believed them(unlike most of America).
To begin with ever since 9/11/01 al Qaeda has exhibited terrible tradecraft, or to put it another way if someone who smells like the typical RIF and has ANY accent and is asking where he can buy the fully automatic weapons without a background check he's going to be lucky if all that happens is people getting the police called on them. To say the least Gadahn would not fit into the crowd at a gunshow.
Secondly the transfer of Class III weapons especially full autos doesn't work like that. Such rare, expensive, and already illegal to transfer via private property sale.
Lastly unless someone is very trained automatic weapons are LESS effective every shot but the first tends to only threaten the air. If the Tuscon psycho had had a full auto we would probably only have one not seventeen dead people to seek justice for.
I shouldn't complain about my enemy doing stupid things though and fully automatic firearms in the hands of your typical RIF are some of the most ineffective weapons since french all-terrain horseshoes.