A short barrelled shotgun or short barrelled rifle can be legally owned, you just have to pay a tax stamp on it. $200 was a LOT of money when Miller passed, not so much these days.
That doesn’t even get into “Non-NFA Firearms” that are designed by the manufacturer to ride the line between legal and illegal.
For example… If you take a Mossberg 590 shotgun and chop the stock down to a pistol grip, and don’t pay the tax, that’s a felony.
If you take a Mossberg 590 and shorten the barrel too much without paying the tax stamp, that’s a felony.
The 590 Shockwave is a “Non-NFA firearm” that is perfectly legal without a tax stamp even though it has a pistol grip and a short barrel.