AR-15 owner - If the lower receiver can be slightly modified to accept an ar-15 upper, then I can understand the seizure. You can buy every piece of an AR-15 without a license, with the exception of the lower receiver which is a single piece of metal. If minor retooling makes these lower receivers viable, then congrats ATF, job well done. [From Comments]I can almost understand Fudds. Almost.
This I just don't get.