I am not an Omega shooter, but I do shoot a T/C Black Diamond XR. Are you swabbing between shots? If your not, this might be a problem. Are the projectiles loading hard? Are you shooting off a nice clean oil free barrel? Are you a bore butter user? Do you lube the sabots because you're not supposed to? Do you seem to be getting good ignition off the Clean Shot pellets? (They must be old pellets to still be Clean Shot)

Normally the Thompson Center brand of projectiles shoot very good out of the T/C rifles. I can push the shockwaves as much as 120 grains and they still hold a great group.

I would personally switch to a loose powder, although a lot of people shoot pellets. My worry with the Clean Shot pellets are they might be old and not consistant anymore. I would get some Triple Se7en loose and shoot that.

Some other projectiles to try are the Buffalo Bullet 375 grain SSB sabots. They shoot fantastic out of all my rifles. I also shoot a 460 grain No Excuses Conical with excellent results. I only push them with 80 grains of Goex FFFg but that is plenty.

Good luck with your rifle...