18USC922 (o), 922 is where a lot of the gun laws reside.
(1) Except as provided in paragraph (2), it shall be unlawful for any person to transfer or possess a machinegun.
(2) This subsection does not apply with respect to -
(A) a transfer to or by, or possession by or under the authority of, the United States or any department or agency thereof or a State, or a department, agency, or political subdivision thereof; or
(B) any lawful transfer or lawful possession of a machinegun that was lawfully possessed before the date this subsection takes effect. "
Technically, the MG ban was not part of any "crime bill", it was the "Hughes Amendment" tacked onto the Mclure-Volkmer reform act that banned new machine guns. The rest of the bill was actually a good thing for us gun owners.