I have spent countless hours trying to answer that question... I found the answer

I got a fixed barrel pneumatic 2289. I'm not kidding, I had a 250 dollar beeman that only shot 495fps and I got the same results you are getting. After trying different pellets, crown, shimming and such around break (break barrel by the way) I shrunk my groups from 2 inches at 60 feet, to 1.75 inches. Haveing a long vertical spread is most likely from inconsistant barrel lockup. If you think about it, your barrel will always be pointing slightly higher or lower than the previous shot because it is on a hinge. A new oring can sometimes help a little. good luck though, there are lots of people who have breakbarrels and get decent groups.

andy