JEFFERSON CITY, Mo. — The Missouri Supreme Court will hear arguments Monday in a case challenging a new gun law opponents say bars police from helping enforce certain federal firearms laws. The Second Amendment Preservation Act, which went into effect in August, declares “invalid” many federal gun regulations that don’t have an equivalent in Missouri law, including statutes covering weapons registration and tracking, and possession of firearms by some domestic violence offenders. Local departments are barred from enforcing them, or risk being sued for $50,000 by private citizens who believe th…