U.S. Code, Title 18, Chapter 44 (Firearms), Subsection 921:
( 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.
This laws within this chapter is also what killed Barrels of America's "The Concealer" barrel due to it technically being defined as a silencer.
Has anyone had any experience with legal issues of the Tippmann C3, or has some evidence/rulings that show that the C3 is not classified as a firearm?