So, please explain your comment about most guns going south?
I suppose I stand corrected.
The Border Patrol specifically states, however, that they are looking for drugs coming North, and Guns and Money going South. Beyond that, I don't really have a comment.
However, my original statement was in how weapons get into criminals hands. Most armed robbers don't get M16's from Zeta cartel. They get their Glock Foh-tay from law abiding John Doe...either from stealing it, or making him think they're a good law abiding citizen and buying from said John Doe. In that respect, the guns going south comment isn't really pertinant, and I probably shouldn't have even mentioned it.
EDIT: I'm not sure where NFA firearms entered the discussion by the way. I was talking about guns getting in the hands of criminals through theft, and through law abiding citizens. Most armed criminals don't have NFA guns. Some certainly do, I'm sure, in the way you're showing, but the VAST majority of criminals guns come from people like you and me.