This rather serious report should be of interest to LW. It argues that autonomous robotic weapons which can kill a human without an explicit command from a human operator ("Human-Out-Of-The-Loop" weapons) should be banned, at an international level.
(http://www.hrw.org/reports/2012/11/19/losing-humanity-0)
The proposal under discussion has poor definitions, but "autonomous robotic weapons which can kill a human without an explicit command from a human operator" is a good start.
That's at least six different grey areas already (Autonomous, robotic, weapon, able to kill a human, explicit, human operator).
My guess is that bullets fired from current-generation conventional firearms aren't robotic, and also don't pass the explicit command test. That is despite the fact that many firearms discharge unintentionally when dropped- a strict reading would have them fail that test.
Finally, the entire legislation could be replaced by legislation banning war behavior in general, and it would be equally effective.
Is this true? My impression is that almost all modern firearms are designed to make this extremely unlikely.