As you say this is not a black and white issue. I would feel very comfortable being in court justifying a grip that was an inch longer. Maybe two inches longer. Possibly three, etc.
You would? Well, 'Bully for you!' as they say. May ye have the very smartest and slipperyest of lawyers!
Two inches? Maybe three? If you come to the attention of law enforcement and they're aware of what you're doing, you'll be tried. If this goes to trial, you'll be convicted. If convicted, you can appeal until the money runs out. I was halfway serious about test cases. If you really feel this is worth fighting, you really could spend about the next decade fighting the battle of trial and appeal to prove just how many inches longer you could make the "nada-stock" before you've "redesigned" it to be fired from the shoulder according to a fair and impartial jury.
Once more, laws don't have to spell things out in fractions of an inch. In fact, they rarely do. They have to speak to actions and intent, and a jury will be asked to find fact -- did you or did you not, IN THEIR OPINION, a) redesign this weapon, and b) do so in such a way that it could be fired from the shoulder? They will form an opinion on those two points and you'll go to jail (or go free) based on their decision.
What I won't buy is some of the reactionary bunkum that some felt the need to spew out at my question.
Look, you don't like the answer. You're reacting badly to the answer. You want to be smart enough to out-think the BATFE and find your very own loophole. But the things you're founding this theory on don't hold up. The factors you think are critical (exact length and what you say you'll claim to be shoulder-able) aren't critical at all. And you're deriding the clearer view of others who understand why this would indeed make you a felon if you proceed.
You can claim anything you like too. The aggressive/negative/ignorant tenor of some comments on my question where not helpful.
No need for aggression, but there's no need for such an assertive and aggressive defense of your clearly, plainly, flawed idea, either. You've asked for insights. You've been given VERY knowledgeable insights and have rejected them, then claimed that everyone ELSE is being ignorant! Surely the irony is not lost on you?
I will say that you came the closest to actually answering my question.
Yes. That's because I HAVE answered your question, as completely as you're likely to get outside of 1) paying a gun law attorney to explain it to you (and trying not to argue with them when they tell you you're wrong) or 2) an up close and personal trip through the justice system.