This is the first I’ve heard that the gun had M-16 fire control parts. If so, that’s a whole different ball game.
The original defense claim, as I recall, was a worn/malfunctioning sear.
Indeed. As Paul Harvey would say, we are now hearing "the rest of the story."
From what I’ve gathered, this case amounts to a “deliberate malfunction”: the gun has all the full-auto parts except the auto-sear, he knew that putting the selector switch in the third (!!!) position caused it to “double” (then jam), and instead of fixing the “problem” he would explain it to people he loaned the gun to. It’s that final bit that actually got him in trouble: the other issues could be explained away in court as an excusable “malfunction”, but he was “transferring” a gun known (intended?) to “double” (technically a machinegun) to other people without filing a Form 4.
He knew what he had, and failed to hide behind the “malfunction” claim; instead of fixing it, he reveled in it. Being stupid in court didn’t help.
That said ...
Yes, the BATFE apparently behaved reprehensibly as well. Nonetheless, he was willfully & criminally stupid. Both sides did wrong, but even if the BATFE behaved perfectly he’d still be convicted.