This may assist you with an answer:
Refer to the question:
Q: Is it legal to assemble a firearm from commercially available parts kits that can be purchased via internet or shotgun news?
BATFE Frequently Asked Questions.
NRA Chief Range Safety Officer, Home Firearm Safety and Basic Pistol Instructor
"There are three classes of people: those who see, those who see when they are shown, those who do not see."
Leonardo da Vinci