For those who get into the world of battle rifles - particularly AK-style - you're going to find yourself having to deal with Federal regulations. Specifically, compliance with 18 USC 922R.
There's lots of debate about what is and is not covered under 922R. I am not a lawyer, but I'm going to present my layman's understanding and interpretation of the compliance requirements. These are my opinions only -- and I don't encourage anyone to take a legal stand based on them.