I also shoot the SW-250 in my Omega however I use 2-50gr-777 pellets vs American Pioneer. I have heard from many that the SW250 with 100-110 grains of powder is a sweet combo for Omega's. I have read good and bad press on the American Pioneer powder.
I am currently getting 1.50-1.75 groups at 100 yards. Certainly good enough for hunting however I believe this gun can do better. The Omega is one helluva gun capable of sub moa groupings once you find the bullet/gr recipe. I am going to give Blackhorn powder a try when I shoot up all my pellets.