So I’ve got a issue I need opinions on resolving.  I recently got my Omega and am running into a mounting issue.  On one sbr I went with a rail slightly longer than the barrel.  The asr mount is binding on the inside of the rail before it bottoms out on the barrel threads.  My first thought is to put a threaded spacer on to make up the gap(as opposed to buying a new barrel or taking a dremil to the inside of the rail and modifying it).  I just want to make sure the mount will have sufficient thread contact so I don’t screw up my can.  Thoughts?

Without measurements or pictures it is hard to know if a muzzle device spacer will make any difference; however, if whatever spacer you use isn't squared to the shoulder it may cause you to have a baffle strike. I wouldn't suggest that method. Sounds like you need a shorter rail, longer barrel, or take off some of the inner diameter of the current rail.

How slightly?

If the Omega mounts fine direct thread then the Dead Air Key Mo mount might be useful, but not cheap.  I had the same issue a few years back and resorted to a shorter handguard. Grow another upper out of the orphaned handguard.

I would sell the handguard on the ee and buy a shorter one. I would not trust the spacer. You could grind down the handguard and rattle can it on the cheap.