How are lower receivers classified legally?

[bluedog]

I'm planning to build an LMT, and have come upon this question. Once I take possession of the lower, is it considered to be a rifle, and does this vary from state to state? If it is not a rifle, will I have to get it re-registered once it is mated to the upper as a complete unit?

[Joe R.]

The lower is the rifle and you will have to fill out all the appropriate paperwork when you pick it up.

[MtCarbine]

Lower can be either a pistol or rifle , all depends on how it is logged into ffl books and how it is disposed of on your 4733 form when you purchase said lower