The DD Omega has the tightest inside clearance of ANY rail/FF tube I've ever seen. I can shave and do so many times per month FSBs to fit under many FF tubes/rails. Steve probably does similar to what I do. I use a plasma cutter, a grinder, a disc sander and a bead blaster, then coat with Norrels moly resin. This is what mine look like.
http://img.photobucket.com/albums/v4...vedFSBs008.jpg
http://img.photobucket.com/albums/v4...vedFSBs003.jpg
The shaved FSB all the way on the right will fit under a DD Lite Rail, RISII, LaRue, YHM and most other rails. It will BARELY fit under a DD Omega and when it does all it takes is you to hit the rail firmly with your hand and it'll run into the gas block.

