I live in Florida and recently bought a stripped lower. I was going to buy through my friend who owns a shop in Georgia, but he told me that stripped lowers are now classified as 'other' by the ATF (according to the agent he contacted) and therefore he could not sell it to me since I'm a resident of another state. When I ended up buying one from a shop in Florida I heard the shop owner call it in as a long gun though, so I'm not sure what's going on with them.

