Yup
@Bassbob, that’s the correct way to go. I came across 2 separate articles on the net, (3 if you count the one previously), that also said to keep the barrel under 16” for AR pistols. The ATF seems to have classifications depending on length, etc.(Any Other Weapon (AOW), Non-NFA weapon, Firearm), It’s similar to the ATF Classifying the Mossberg Shockwave & Remington TAC13 & TAC 14 “Firearms” and not shotguns, because by their definition, a shotgun must have a stock (instead of the bird head grips these two firearms use). Many people have different interpretations of ATF regs & it’s prudent to do ones research delving into these type of builds as you say.