FX BOSS problem! SOLVED, Thanks to all of you!

Having trouble with my FX Boss. Been running it over the chrony & adjusting HS from all the way down (tight) to zero spring tension at all. It only shoots from around 440-505fps. Any thoughts, suggestions or similar experiences? I'm all ears for your collective wisdom!
Any idea what the regulated pressure is? I have a fitting that screws into the stock screw adapter that has communication to the plenum pressure. I used it on my Royale's to check the pressure. If I can locate it you're welcomed to it.
 
Maybe another option? Barrel misaligned, causing a dwarfed transfer port.
YOU, my friend were CLOSEST to the solution! Three screws hold the barrel in place. Screw #3 that locks the brass transfer port in place didn't get tightened down after the last work done on the gun. Brass collar with transfer port on bottom rotated while the REST of the barrel was locked down securely. THANKS for the suggestion!
Any idea what the regulated pressure is? I have a fitting that screws into the stock screw adapter that has communication to the plenum pressure. I used it on my Royale's to check the pressure. If I can locate it you're welcomed to it.
Thanks so much for your offer but problem solved.