Look at the pricing. The average world price for an AK-47 is around $150. That would have to mean that the supply is virtually unlimited. The AK is one of the most reliable weapons ever made. NOBODY could make a profit transporting weapons from the US and selling them there for that price.
So, why buy an M-16 when you can get an AK that cheap?
You made the claim that the M-16 was not the most common weapon found. (it is also not the only U.S. made military rifle either) Many FReepers have been working hard to find out what is being found and where it came from. If you have information about that please share it with the forum.
I will also repeat what I said about that in the first place. Free is still cheaper than $150.