[bargle0]

This was made before 1899 (or whatever the cutoff date is), and it’s black powder. The ATF does not consider this a firearm.

[dmoy]

Pedantically, it would be considered an "antique firearm". Still a firearm, but basically unregulated

[voxic11]

> (3) The term “firearm” means (A) any weapon (including a starter gun) which will or is designed to or may readily be converted to expel a projectile by the action of an explosive; (B) the frame or receiver of any such weapon; (C) any firearm muffler or firearm silencer; or (D) any destructive device. Such term does not include an antique firearm.

according to the law antique firearms are not firearms.

[15155]

Black powder deflagrates, it doesn't detonate (explode.)