HB 436 in part says:

“All federal acts, laws, orders, rules, and regulations, whether past, present, or future, which infringe on the people’s right to keep and bear arms as guaranteed by the Second Amendment to the United States Constitution and Article I, Section 23 of the Missouri Constitution shall be invalid in this state…”

Story and full text of the Missouri bill at the 10th Amendment Center blog:

http://blog.tenthamendmentcenter.com/2013/02/missouri-legislation-would-nullify-federal-gun-laws/