I agree with Backwoodsman that the heavy automatic weapons should be banned, but the problem is complicated by the States' different regulations.
There would seem to be a Constitutional conflict, and the Supreme Court could uphold the States rights to decide, if the Federal Congress ever passes a bill outlawing them.
Would the change make any difference? Gun-involved homicides are not carried out with heavy weapons; only the so-called "militia" types would be affected. Members of these groups are a threat, at least in my mind, but gun-related homicide statistics would be little affected.