I went with the Burris AR332. Its not an ACOG...but its pretty close and in some ways better (I prefer the Burris reticle). Very good optics. I torture tested mine and it proved to be quite rugged. Costs about $315 bucks +shipping on Amazon.
I removed the rails from my scope.
http://www.amazon.com/dp/B002QEUPEE/...SIN=B002QEUPEE