Tippmann A-5 Velocity Troubles

I have a Tippmann A-5 with a Flatline barrel, and cannot get the Velocity high enough to have the flatline perfom at its optimal fps, let alone get any accuracy at all. i have played at a field once, and the employee cold not increase the velocity of the marker over about 220 FPS. I checked the power tube for a problem as, but did not find any cracks. could there be a problem with the spring? i think my gun was shipped cocked for over two weeks or so, because when i took it out of the box, i pulled the trigger and the parts inside engaged like if you cock it and dry fire it, but i had never pulled back the lever( i dunno if this would affect the spring or not)