Interesting gun-sales legal case and a more interesting explanation.

[Edward Tinker]

Originally Posted by Vlim

The 'receiver' bit is funny.

Just about any country I know identifies barrel, receiver and frame as essential gun parts.

In the USA - where the bolt goes is considered the receiver, but for pistols, the 'frame' is the part considered the legal part, NOT the upper receiver. The issue I see with something like this is that all major parts could fall under ATF purview, so uppers, frames, bolts, etc.