It's an AOW under the NFA even though it doesn't accept fixed ammunition and doesn't fire through the stalk in the traditional way. If it is bored through to the touch hole on the breech end it is functional. Perfectly legal under Federal law for any lawful citizen of the USA to make for their personal use, IF the proper paperwork is filed and approved by the ATF beforehand. Many state and local jurisdictions prohibit possession of otherwise lawfully obtained NFA items, check with your local head of law enforcement (police chief or sheriff) before filing.
From the NFA Handbook, chapter 2.1.5: Any other weapon. Firearms meeting the definition of “any other weapon” are weapons or devices capable of being concealed on the person from which a shot can be discharged through the energy of an explosive. Many “any other weapons” are disguised devices such as penguns, cigarette lighter guns, knife guns, cane guns and umbrella guns.
