I need to ask a dumb question. They call this a "stand alone" sight. Does one still have to have a front sight mounted? I have an AR10A4 flat top with an ACOG on it. I wanted a back up, just in case. However, if I have to buy a matching front sight for a 40, then it doesn't do me a lot more good than the detachable carry handle and front sight. If it can work alone, then I would be interested.