Welcome to the forum it is good to have you here..

What will work in your Omega is hard to say. I have a Black Diamond XR. Same barrel, but different action. With loose powder I shoot 110 grains of Pyrodex RS or Goex and a 250 grain Shockwave with excellent accuracy. With pellets, I actually got good accuracy with three pellets and a 250 grain Shockwave. It also does well with just two pellets.

I would stick with the 2 pellet so of Triple Se7en and a 200, 250, or 300 grain Shockwave. You could also try some 240 & 300 grain T/C Mag Express XTP's. They should shoot well. Nosler, Speer, Barnes, Parker, are also good choices. As for powerbelts, while your rifle will shoot them, I would stick with a sabot load.

Good luck with your rifle. Keep us posted on how it does for you.