Ar15 plus machine shop equals M16 in 20 minutes.
You know, I see antis make that same argument but I've yet to see the machine shop that can put metal back onto a bolt carrier, hammer, sear, trigger and disconnector. I guess they could always machine their own M16 parts and add them to an AR15; but that is certainly not a 20 minute job and any machine shop sophisticated enough to do it will have no problem producing automatic weapons from scratch.
The government is already sharing NICS data with the Mexicans and has been for several years now. We already have the laws in place to stop this, all we need to do is enforce those laws. We hardly need new ones.