Anyone know the rules on this? Can I buy any reciever ie: ar-15 or ak47, and build a gun. I am looking at buying an AMD parts kit for $180 and a reciever for less than $100.....Put it together and I have a $300 AK pistol? Can I do the same with the AR lowers and buy the 10" upper for SBR's or pistols and have a National Match trigger AR pistol? I have the Bushy Carbon 15 pistol, It says "PISTOL" on the receiver. Does the reciever I buy have to be designated as a pistol?.......Thanks!