When I beat general RAAM on insane what I did was play co-op. Before going into the fight by pressing the button, get a torque bow and a sniper rifle. Dom also had a torque bow. When the fight starts stay behind the cover that you start behind and stay there the whole time. There are a few ways to do this: You could have Dom just heal you if you die or you could both join in the fight (this might be more risky).

When the fight starts shoot RAAM with the torque bow so the explosion scares away the Krill then shoot him with the sniper rifle.
After this he will enter light and send the Krill away himself. Shoot him 2-3 times with the sniper during this time. Now, if you get lucky (this may take a few tries) RAAM will move to right behind a box to the upper right(it is in front of another box and is small).
When he goes there he is glitched, and will not move. Just stay behind the cover the whole time and he won't leave.
Now shoot him with the torque bow and then the sniper rifle. If you run out of torque bow arrows use grenades to clear the Krill or better yet have Dom use his torque bow.
If you die from RAAMs shooting simply have Dom get you up, and that's why you should co-op.
Shoot RAAM about 16 times with the sniper rifle to finally kill him.
Using this I finally beat Gears of War on insane difficulty.