Can someone tell me how to get past the ogre, I have used over 100 rockets on it and its only down to about 80%.

Thank You

When he lifts his arms up to throw the rock at you fire at the glowing thing on his belly, if it hits the spot he'll stop and get a bit closer to you and start hitting with his fists, when he stops he bends forward and pauses,
then you need to hit the glowing spot on the top of his head.
Rinse and repeat, only needs three good hits and he's down.

Although be aware that hitting the glowing spot under the arm is not an exact science (xbox) it seemed easier firing from the left side of th screen.

fire from the left and shoot from the hip.

Shoot from the hip. By doing that you can see all of him instead part of him through the scope.

I used the sights. Strafing slowly on the right was enough to avoid being squashed. You have to time it a bit before you actually see the target, so learn the timing and anticipate.

To me it was obvious you shoot the glowing blue spot on his chest, then the one on his head when he bends over in pain.

The part I didn't see right away is that you don't really hit the one on his chest unless you time it just right. If you wait until you SEE a clear shot at it, you most assuredly won't get an effective hit. Instead you need to time the shot so you shoot just before that spot on his chest becomes visible, because the rocket takes a moment to get there.

So essentially this is not a shoot the secondary spot numerous times to make him bend over and show the primary spot thing. It's a time the shot properly at the secondary spot strategy, which allows you to do it in one shot. Trust me, you will NEED to do it this way if you expect to beat him on nightmare mode.