If you buy a stripped lower marked "other" on the 4473 form by the dealer and put a short barrel on it....is it a pistol??
More or less, yes. Keep in mind, I'm not an attorney, nor did I stay at a Holiday Inn Express last night.
If you set it up as a rifle, it's a rifle, and must remain as a rifle.
Set it up as a pistol, it's a pistol, and must remain as a pistol.
I asked an FFL about it this weekend and he said the label the stripped lowers as "receiver" on the form.