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)

Buy a spring kit and replace the spring and if that does not fix the problem change the END CAP completly and see if then your problem gets fixed.

I had a similar problem on mine, but mine was that i could not lower the velocity, i would adjust it and it would go back up even with the FVA screw all the way in. It was the end cap which we noticed because it fell apart when firing the gun. I had bought it used also, so check that and get back here and lets us know if it worked or not. Hope it helps