Originally Posted by
buckengr
This is correct. Present configuration is what matters, not what was checked on the 4473.
If it has a rifled bore, the overall length is > 26" and it is not intended to be fired from the shoulder, it is a "firearm" when equipped with a vertical foregrip.
It is not a rifle because it is not intended to be fired from the shoulder -- nor is it an SBR for the same reason.
It is not a pistol because in this case it WOULD have a second vertical grip which would mean it is intended to be fired with two hands.
It is not an AOW because the overall length is >26" which is the constraint that the ATF uses to determine whether a firearm that doesn't meet any of the other criteria is "concealable".
So provided that the lower you are using was not INITIALLY assembled as a complete rifle, it would not fall under the weapon made from rifle criteria which would require registration as an SBR. Therefore the firearm you describe would be considered simply a firearm when equipped with a vertical foregrip.
This assumes, once again, that the overall length IS INDEED over 26".