United States v. Stewart, 348 F.3d 1132 (9th Cir. 2003) and 451 F.3d 1071 (9th Cir. 2006), is a Ninth Circuit case involving a challenge to the constitutionality of 18 U.S.C. § 922(o) under the Commerce Clause of the United States Constitution. The United States Court of Appeals for the Ninth Circuit found against the defendant, ruling that possession of homemade machine guns can be constitutionally regulated by the United States Congress under the Commerce Clause. Background Robert W. Stewart, Jr., a convicted felon, sold parts kits to make Maadi-Griffin .50 caliber rifles, which he advertised on the Internet and in Shotgun News. A Bureau of Alcohol, Tobacco, Firearms, and Explosives agent discovered that Stewart had a prior conviction for possession and transfer of a machine gun 18 U.S.C. § 922(o) and began an investigation. An undercover agent purchased kits and determined that it could be "readily . . . converted" into an unlawful firearm, in violation of 18 U.S.C. § 922(a)(1)(A) and 18 U.S.C. § 921(a)(3)(A). The ATF agent then applied for and received a federal search warrant for Stewart's residence. During a search by the ATF of the Stewart Residence, agents discovered thirty-one firearms, including five machine guns which Stewart had machined and assembled. In United States District Court for the District of Arizona, Stewart was convicted of one count for being a felon in possession of a firearm under 18 U.S.C. § 922(g)(1) and 18 U.S.C. § 924(a)(2), and five counts for unlawful possession of a machine gun in violation of 18 U.S.C. § 922(o). On June 3, 2002, Stewart was sentenced to five years in federal prison. Stewart appealed his conviction under 18 U.S.C. § 922(o), claiming it exceeds Congress's commerce clause power and violates the Second Amendment, and for possession of a firearm by a felon on Second Amendment grounds. Circuit Court On November 13, 2003, the Ninth Circuit Court of Appeals issued an opinion vacating Stewart's conviction for violating 18 U.S.C. § 922(o), but affirmed his convictions for being a felon in possession of a firearm. Using the Morrison test, the Ninth Circuit ruled 18 U.S.C. § 922(o) did not have a substantial effect on interstate commerce and was unconstitutional as applied. In its opinion the circuit court wrote: "...a homemade machine gun may be part of a gun collection or may be crafted as a hobby. Or it may be used for illegal