RE: tc omega groups
Have you thoroughly cleaned the packing/shipping lube from the barrel?
If not, then I would suggest a good bore cleaner (Butch's Bore Shine and so on) along with brass brush. Really work the bore with a good solvent to get the packing lube out and get the bore very clean. No lube on sabots. Bone dry.
Next in order to ensure tighter grouping, you may need to swap in between each shot depending on your rifle, the projectile and the powder your are using.
I'd try these two things first before I purchased different bullets or powders.