Writing today at the National Review Online's The Corner Kevin D. Williamson was critical of organizations, including Media Matters, for highlighting Al Qaeda spokesman Adam Gadahn's recent video instructions to purchase guns at gun shows to use in terror attacks against Americans. From Gadahn's statement:

America is absolutely awash with easily obtainable firearms. You can go down to a gun show at the local convention center and come away with a fully automatic assault rifle, without a background check, and most likely without having to show an identification card. So what are you waiting for?

Mirroring common gun lobby talking points Williamson notes that “fully automatic” guns are highly restricted and regulated. Williamson's account is in fact a highly misleading characterization of the accessibility of fully automatic weapons. The reality is that semi-automatic rifles, such as AK-47s or AR-15s, are widely available and sold at gun shows from private sellers that do not run background checks. Further conversion kits that make these rifles indistinguishable from machine guns are also widely available at gun shows.

Williamson's focus on the availability of fully automatics weapons distracts from the uncontested fact that terrorists could easily use gun shows to bypass background checks as they plot the next Mumbai style terrorist attack.

From Williamson's post:

In his latest statement, Mr. Gadahn repeated the myth that machineguns are widely available to American civilians, and he encouraged his fellow jihadis to hit the gun-show circuit and gear up for an intifada in the United States. When I read that statement, I was certain that it would be repeated as fact by the antigun ideologues and their enablers in the media. [....]

It is not easy for a U.S. civilian to legally possess a “fully automatic assault rifle,” or any fully automatic firearm at all. If that civilian is not a federally licensed firearms dealer, owning a fully automatic weapon manufactured after 1986 is categorically illegal; fully automatic weapons that were legally owned and registered with the federal government before 1986 may be transferred to a qualified buyer with the approval of federal and local law-enforcement authorities, a rigorous background check, and, of course, a sign-off from the U.S. Treasury Department: there's a couple hundred bucks in fees and taxes involved. (You may examine the application here.) Selling a fully automatic weapon to an unlicensed party, at a gun show or anywhere else, is a very excellent way to land yourself in prison for a good long while. Mr. Gadahn, and the editors of the New York Daily News, are full of it.

Also writing at The Corner Clifford D. May noted the availability of conversion kits fact in a post responding to Williamson:

That's not correct [Gadhan's assertion regarding the availability of fully automatic weapons], as Kevin makes clear. A fully automatic assault rifle -- or any fully automatic firearm -- is very difficult to acquire due to serious restrictions already in place. But one can, I believe, buy a kit that will enable the conversion of an AK semi-automatic into a fully automatic weapon.

Conversion manuals are easily found online and a General Accountability Office investigation found that investigators were able to obtain all of the parts necessary to convert a semi-automatic AR-15 to a fully automatic M-16 at gun shows in five states. Conversion kits are quite popular at gun shows. Mark Potok, director of the Intelligence Project at the Southern Poverty Law Center found conversation kits were, "all over the place at gun shows". Potok said in an interview with Omar Samaha of Fix Gun Checks:

I went to quite a few guns shows in the 90s during the first peak of the militia movement and they were really remarkable place to visit. First of all they were filled with all kinds things that were not quite legal. I'll never forget these very cheap little kits that essentially were kind of gloried rubber bands. Which for a for dollars you could convert a semi-automatic into a completely illegal full automatic weapon. But you'd see that all over the place at these gun shows. Including huge shows in places like Houston where you'd have 400, 500, 600 tables.