To amend title 18, United States Code, to impose mandatory prison terms for possession or use of a firearm or a destructive device during conduct constituting a crime of violence or a drug trafficking crime under State law.

Amends the Federal criminal code to establish the following penalties, in addition to the punishment provided for the underlying crime, for engaging in a crime of violence or drug trafficking crime (including such a crime which provides for an enhanced punishment if committed by the use of a deadly or dangerous weapon or device) for which the perpetrator may be prosecuted in a State court. Provides that whoever: (1) possesses a firearm shall be sentenced to imprisonment for ten years without release; (2) discharges a firearm with intent to injure another person shall be sentenced to imprisonment for 20 years without release; or (3) possesses a firearm that is a machinegun or destructive device or is equipped with a firearm silencer or muffler shall be sentenced to imprisonment for 30 years without release. Sets penalties for second, third, and subsequent convictions. Prohibits the release of any person convicted for any reason during a term of imprisonment imposed under this Act.

Specifies that, except in the case of a person whose criminal conduct gives rise to the use of a firearm by such person, this Act shall not apply to the conduct of any person in defense of person or property during the course of the commission of a crime by another person.