you want speed, power, and accuracy out of the Omega's and other rifles I would go with a 250 grain Shockwave. They should shoot real flat, hold way out at distances, and still have excellent knock down power. 150 grain loads are possible, but usually they find that with pellets. If your going to shoot loose Triple Se7en or Pyrodex you might want to look into the 110-120 grain range. The speed might not be there but it should be all the bullet you would need out to those distances.

I was shooting one afternoon at a paper plate at 150 yards with my Black Diamond XR. I was surprised at how easy it was to hit that paper plate off a set of shooting sticks. I think it took me two shots to figure out the drop but after that the rest was easy. I never did try to get back further then that.