The Gun Control Act defines "firearm" as:
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.
It doesn't use an explosive propellant -- it is not a firearm, and the ATF has no authority to regulate it.
I think it might qualify as D) a destructive device.
What I want to know, is how does non ferrous projectiles, such as aluminum, work.
Too many words, man!!
“...shall not be infringed.” = the ATF has no authority to regulate SH!T.