SBR and AOW are regulated by the NFA of 1934 which is still in effect. Regardless of what wording was in the AWB it expiring did not change anything.
Pistol + Stock = SBR
Pistol + Forward grip = AOW
A receiver does NOT need to be "marked" pistol. Any receiver that has not had a barrel installed is not yet a rifle or pistol and can be built into either. Once a barrel is installed it is the a rifle or pistol forever.
Originally Posted by ofitg
UPDATE - I think I found the answer - the 1927A5 had a 13 inch barrel, giving it an overall length of 26 inches - supposedly, this overall length made it exempt from AOW status
Correct. Read this ruling letter