**DISCLAIMER: I fully understand the general legal issues that go along with machineguns, and the fact that NFA rules make it illegal to produce a machinegun or obtain one made after 1986. This question was just based out of a hypothetical discussion I had with another shooter the other day** This question is more of a technical one, just for the sake of curiosity... a friend and I were recently talking guns, and how it seemed like things like auto sears (or parts kits containing them) were commonly sold at the gun shows we remember going to 10-15 years or so ago. Neither of us has seen one around in a while, though neither of us really attend gun shows these days, nor have we ever looked for the parts since neither of us can afford a pre-86 M-16. But, as a matter of legal discussion, we started debating the current legal situation, and were wondering where things stand from an ATF perspective on these parts. Thus, the following questions: 1) Are auto sears for M-16 style rifles now considered an NFA part that needs to be tax stamped in and of themselves? If so, what became of all of those parts kits we used to see at gun shows? Are those all considered unregistered machine-guns now? 2) Or, are auto sears still just part of a parts kit that really has no relevance other than the fact that they can only be installed on a properly registered/tax-stamped NFA lower receiver (one of those elusive pre-86 lowers with the proper design to accommodate the auto sear)?