Elkins45, a truely manly statement there with the duct tape. Kudos to you. If you can't fix it, "duct" it.
Here's a less sticky way of doing it:
http://www.mountsplus.com/AR-15_Acce...CDM-MOD-C.html
Clamps on the barrel/mag and clamps on the light. Little more stable and keeps the light more parallel to the barrel than duct tape.