I have an SW5 and am considering purchasing a collapsible stock. Given overall weapon length legalities, would I then be required to register the weapon as a "pistol?" Since the barrel length would yet be 16" I wouldn't think this would be deemed a SBR. Or, would adding a collapsible stock somehow be in violation of 922(r)?
adding a collapsible stock would be a violation of the Assault weapons ban.
And just for your future reference, the ATF's definition of a pistol is any weapon that can not be fired from the shoulder(ie, no stock). and for that matter, once a weapon is assembled in to a "rifle" (one that has a stock) it can not become a pistol. So, technically, you can have a 16" barreled pistol.
and if you do have a firearm that is registered as a pistol to add to the confusion, if you have a vertical foregrip on your forend, it may be considered to be an AOW(I'm not sure if this issue has been cleared up yet or not.) Oh yead, on a pistol, their can't be anything encircling the barrel that would act as a barrel shroud, which would make it in violation of the AWB, unless of course it is a pre-ban, then you need not worry about that part.
Alright, I think I'm done now. Confused? I know I am