Try upping your CDEL setting, which may help over come a problem with your reg...try borrowing a reg or adjustable air system from someone and fit taht direct to teh vert mount to see what happens.
CDEL is teh delay, between your gun firing and the re cock sequence starting, blowback and shootdown are signs of too short a dwell setting...QEV's and 44 Ram?
Also..if your COFF time is too low, that may cause shootdown, because teh gun will be firing again before teh bolt has fully closed.