I never tried tuning my QB78D to that power level so can't say for certain. The best I could manage with a 20fpe, and considering the inefficiency of the shortened barrel of course, was 8 shots per 1,500psi fill. At a wild guess perhaps 12 to 15 shots within 4% ES, with a careful job of tuning it? Just a guess though.
You have not be too fare from true. After filling exist reservoir up to 1500 PSI I did 10 shoot to 600 PSI. The speed of 0,510 gram JSB Exact express has decrease from 258m/s to 218m/s within grouping 2 MOA.
I have just now opened transfer port and added one 3mm pad to hammer spring only.If I understand right I have to reduce spring intensity ( remove 3mm pad ) if I want to reach max velocity not at 1500 but at 1200 PSI ?Also speed trajectory will be flatter and efficiency increase ?