Here's an anecdotal look at the weapons smuggling process. A 20-year-old Mexican national was arrested this weekend at the port of entry in San Luis, Ariz. From the Associated Press:
Authorities say a man has been arrested for attempting to smuggle empty assault weapon magazines out of the U.S. into Mexico.
[Customs and Border Protection] say they discovered 80 ammunition magazines for AK-47 assault rifles in his vehicle.
According to the Fronteras Desk story from April,
The ATF notes that criminals used rifles more than any other type of gun, especially the AK-47 and AR-15 variants.