Stand your ground laws became famous during the Trayvon Martin case, but the name that should really be associated with them is ALEC. The American Legislative Exchange Council is a conservative organization that pushes a host of laws in any state that might pass them. ALEC is the reason that "stand your ground" laws are as widespread as they are.
Montana legislators are rethinking their "stand your ground" law due to this tragedy, but don't expect it to change. Powerful interests will be able to exert their will and keep "stand your ground" in place. Really, if you want gun reform, fight for campaign finance reform.