No doubt, but that is not the same thing as the drug cartels and gangs getting them. They have their own, cheaper and better, sources.
It might be folks wanting some protection *against* the druggies.
Before all our restrictions on firearms for our own people, there's no doubt lots of guns went to Mexico, and handguns as well as some semi-auto rifles likely still do, since they are very difficult to obtain legally there as well.
But all those full autos aren't coming from US guns shops or gun shows. If some are coming from the US, they are stolen, or otherwise diverted, from the military and police.
like I said...believe what you like