Here, if it is made prior to 1898 or maybe it's now 1900 & factory ammo is not available, it is an antique and may be owned by anyone [even those (past criminals) barred/banned from owning firearms], no P.A.L. required.
This gun probably fits the category, but further proof would be needed. My 16 bore Husky M20, with straight rifled barrel meant for black powder low and round ball along with the left being a smooth bore was made in 1902, thus is/was a firearm.