Here's a challenge.........

Walk into your local gun store and ask for an AK-47.

One of two things is going to happen:

The owner is going to politely ask you to leave,

or

If you happen into one of the few gun stores in America which happen to sell AK-47's, you are going to get asked for your FFL Class III license, a $200 non-refundable transfer application tax/fee, and you'll get a bill for about $7500 for the weapon. Some weeks later after all the paperwork has cleared, you'll get your AK-47. Legal fully automatic weapons are rare, dealers are rarer still, and the amount of paperwork required to get the required license limits the number of applicants who are willing to go through the trouble.

If you buy a gun from someone off the street, with no paperwork and no background check, you are committing a felony, with an automatic (theoretically, it's hardly ever enforced) 2 year federal jail sentence.