Have map rotate to be the direction you are looking

The easiest way to pass this point is to grab the LMG and then find cover, you don't actually have to kill anyone. It's all time based (or if it isn't, your squad makes short work of the small amount of people you need to kill), and then a helicopter will fly in and take out the rest.

If it's red that means it detected some other input during the quick time event period. Do you have other controllers attached -- joysticks, gamepads, etc? Anything else that would send an input signal during that interval? FWIW I had no problem with this sequence, though I did mess it up the first time..