So here's the thing. My discussion of Chevron deference started with a discussion of whether a defendant should be allowed to argue that the agency, the ATF here, told him that what he was doing was legal. In no way did I mean to imply that the ATF used some novel, counterintuitive definition to screw an unwitting citizen. That happens....doesn't look like that is the case here. The statute has everything that is needed.
There is no unique definition involved. That is, I don't think they needed an ATF definition to convict on the machinegun counts. Mainly, this is because of the admissions on the YouTube channel made proving the intent of the card so easy.
If you have not watched the video linked above, 5 minutes of Matt Hoover Saying Incriminating Things- watch it and listen carefully, especially at the beginning. While you watch it, keep this definition in mind- this is the statute, not an ATF definition:
"(b) Machinegun. The term “machinegun” means any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger. The term shall also include the frame or receiver of any such weapon, any part designed and intended solely and exclusively, or combination of parts designed and intended, for use in converting a weapon into a machine gun, and any combination of parts from which a machinegun can be assembled if such parts are in the possession or under the control of a person."
26 USC § 5845
Is the metal card with the etching on it "designed and intended solely and exclusively...for converting a weapon into a machine gun..."? There's enough there to let a jury decide without a special definition from the ATF.
"It's just a piece of metal"- sure...so why did Hoover specifically refer to it as having as a "Lightning Link" etched on it? Why did he say: "you have to manufacture it." This is evidence that he knew and expected people to use the card to make a "lightning link" to get to full auto.
Not saying they would not have pursued him anyway, but he talked himself into problems and made proving the "intended soley and exclusively.." part easy. Notice there is nothing in the actual statute that talks about how easily making the part work for a machine gun must be. Just a piece of paper with the same drawing? Probably OK because it cannot be used as a "part". However, the intention is for this very piece of metal to be used as THE part. That's a problem. His statements made it perfectly clear that's what the card was for.
"But what about a blank piece of metal?" Sell a card of metal with no markings on it that is the proper thickness WITH the drawing on paper and see what happens....no, seriously, don't.
Now- nothing I have said here should be interpreted as an endorsement of the law or definition. However, to discuss how the law is going to be (and has been) used, I don't have to believe it's right.
What I get from this is that even if ATF's advice to people was binding, and he had it in writing (or was able to get the agent to testify and confirm that he said it was ok) it still might not save him because the agent would say "yeah but you only asked if you could draw it on metal. You left out the bit about intending it to be used to make a machinegun"