XmrBazaar (beta)

You would have to know your own laws. For example in America you can private sell a gun without an FFL in most states, but if you sell for a net profit or ship it you often need an FFL. Non-registered parts (such as things other than the registered receiver) are not a regulated item. It's the same as a piece of metal. NFA items require a SOT, but components that are not configured or sold in conjunction with other items that imply a constructive intent are not.

For example, this is why you can buy full auto trigger packs online to all 50 states legally (despite what fudds often claim). However you cannot buy that same trigger pack with a functional compatible receiver. You cannot buy full auto parts which are registered by itself as a machine gun. For example you can buy an M16 auto sear, but a DIAS like a swift link (the infamous coat hanger machine gun) is a registered item because it can drop into an AR receiver without the third hole. In contrast the M16 auto sear cannot work without a receiver that has the third hole, which is why there are no legal restrictions on ownership of them.