Aow / Sbs
To be an AOW, it MUST have been shipped from the factoy, with a pistol grip and no stock = shorten below 18" and it is an AOW.
If the shotgun was shipped with a standard stock, when you shorten it below 18", it becomes a SBS = $ 200 Tax.
Pen guns such as the PENFIRE, are an AOW.
Hope that helps !