Ja, ons koop die goed hier soos brood en botter!
I know where you are coming from, I left SA 26 years ago (temporarily I thought..
), and since moving to the US I just cannot stop buying the darn things. There are some states in the US where they have a permit system or waiting period on handguns and/or long arms, but in most free states you can buy or sell a firearm from/to a resident of your state with little restriction. If you pass the instant NICS check or have a concealed weapons permit, you can also buy from a ffl dealer and walk out with it right now, or buy a firearm from a private individual and have it shipped to a dealer. There is no restriction on AR15 uppers or any kind of barrels, the receiver is considered the only registered part here. Same goes for primers and powders, you normally only need to provide a copy of your drivers license so they can verify your age.
Personally when I sell a gun face to face, I'd like to know where and to who it is going. If you are an NRA member, or have a ccw, or been hanging out at the same forums I do for a while, no problem. Seen too many gangbangers in AZ buying every AK and SKS they could get their hands on from private individuals at gunshows, and whether it was legal to sell it to them or not, it was wrong.