http://www4.law.cornell.edu/uscode/26/5845.html
Note the definition of "firearms" in 18 U.S.C. 921 (i.e. the criminal code) is significantly more broad:
http://www4.law.cornell.edu/uscode/18/921.html
Note the lack of "handgun". Does this mean BATFE/Treasury taxation of manufacturers for manufacture of handguns is illegal?(a) Firearm
The term ''firearm'' means
(1)a shotgun having a barrel or barrels of less than 18 inches in length;
(2)a weapon made from a shotgun if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 18 inches in length;
(3)a rifle having a barrel or barrels of less than 16 inches in length;
(4)a weapon made from a rifle if such weapon as modified has an overall length of less than 26 inches or a barrel or barrels of less than 16 inches in length;
(5)any other weapon, as defined in subsection (e);
(6)a machinegun;
(7)any silencer (as defined in section 921 of title 18, United States Code); and
(8)a destructive device. The term ''firearm'' shall not include an antique firearm or any device (other than a machinegun or destructive device) which, although designed as a weapon, the Secretary finds by reason of the date of its manufacture, value, design, and other characteristics is primarily a collector's item and is not likely to be used as a weapon.
Note the definition of "firearms" in 18 U.S.C. 921 (i.e. the criminal code) is significantly more broad:
http://www4.law.cornell.edu/uscode/18/921.html
(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.