To turn that USC into a 9mm UMP, you must perform a caliber and furniture conversion. H&K USC: Civilian Version of the UMP Submachine Gun

For a civilian looking to acquire a 9mm Heckler & Koch UMP, the "story" is one of patience and technical transformation. Because the true full-auto UMP was introduced in 1999—well after the 1986 ban on newly manufactured machine guns for civilians—you cannot simply buy an original factory UMP 9mm for personal use.

: You can find these at major retailers like Palmetto State Armory or on secondary markets like GunBroker . 2. The Transformation: Conversion Kits