re: If you are on the fence about buying an AR

The lower receiver carries the serial number and has to go through a FFL. If you buy a completed lower (lower receiver with all the internals, grip, stock, etc. installed) or a complete rifle, that has to go through an FFL as well.

So, the lower receiver and any part of the rifle sold with it has to go through the FFL. If it's not sold with the serialized lower receiver, then it's parts and parts can be shipped to your front door, at least as far as the feds are concerned.

Basically everything except this can be shipped to your front door unless your state prohibits it.