It seems FTB must have nothing better to do these days than re-read everything they've written over the last decade or so and decide what parts don't fit into the various judicial strategies they'd like to assert.
On September 30 of 2004 I received the ever-famous "string trick" letter declaring a shoestring to be a machinegun. That letter, while new information to many of us, was actually just a re-statement of a determination that ATF made back in July of 1996. So, until just recently, the ATF's position regarding shoestrings had been consistent for nearly 11 years (a surprising feat for ATF in my opinion).
Well, since I heard that the National Association of Criminal Defense Lawyers published a copy of the letter to their membership, and since Halbrook used it to poke fun at 'em at an industry meeting, and since it's been used in numerous court cases with a variety of beneficial effects (in my opinion), I guess ATF got tired of it and decided it was time to re-write it.
Spontaneously (in other words, without any inquiry by me or anybody else that I am aware of) ATF sent me a new letter, overruling their now-nearly-3-years-old letter (link below).
I'm not completely positive exactly what ATF was trying to "fix" with their new letter, but it would seem that it actually should cause them more problems than it solves.
Best I can tell by their new logic, a part that is designed and intended solely for the purpose of converting a semi-automatic rifle into a machinegun is now *not* a machinegun *until* it is added to a firearm. They definitely seem to read the law a lot differently than I do, but that's nothing new.