[cconover]

The only part that is actually considered a firearm under federal regulations is the lower receiver, so it is the only item that is controlled and requires paperwork. Everything else (with the exception of prohibited or specifically regulated items such as suppressors) is a generally available component that does not require the ATF to approve the purchase. Laws state to state on other components may vary, such as magazine capacity.

[throwaway0a5e]

There's still a lot of ways the ATF can show up and shoot your dog if you pick the wrong components and put them together without paying $200 and waiting half an eternity.

[cconover]

The question, though, wasn’t whether ATF agents might interpret the regulations one way or another, but what the regulations are. Millions of people purchase legal and freely available components for their legal firearm with a serial number, and do not run afoul of the law. As soon as we are talking about components or firearms requiring a NFA tax stamp we’re in a different category though.