At the beginning of Mission 14: Into The Furnace, you are only allowed to use (shoot) the laser pointer until you reach the top of the hill. You will get the “Warheads On Foreheads” achievement when reaching the entrance door to the labs (just before going inside the building). You cannot shoot any of your weapons. Equip the laser pointer to request drone strikes. Your drone has unlimited ammo but takes a while to recharge. It is recommended to do this on the Recruit difficulty.