Two options:
1. Could be regulator creep. My Huma climbs to 2200 PSI shortly after fill, but after 1 shot seems to regulate to 2k psi. I hear that creep is less of a problem the more the air rifle is shot. The internal regulator mechanism seats and settles in better with a few hundred shots through it. Mine only has about 120 shots through it, so it is too soon to tell.
2. The O-Rings are leaking on the exterior of the Huma Regulator. This allows some of the 3k PSI air past the regulator and migrate into the gap between the regulator and the valve body. The rate of drift may be an indicator of which of the two mechanisms are at play.
Just a sub-note, the calibrated marks on my Huma has about a 5 bar error. I set mine to 1900 PSI, but ended with about 2000 PSI. Mine will be pulled today (sneaky Pete method), and adjusted down another 10 bar to get it in my new calculated ideal pressure. 2000 PSI ended up being too much pressure. With relatively neutral settings on the WAR SSG (pre-load nut half-way down the threads and with a 0.020 gap on the hammer) I was delivering 55 FPE. I ended up having to set a ridiculous hammer gap to drop it down to 40 FPE (to do a 40 shot string for test), so pre-load will be reduced to get it down to 40 FPE when the regulator pressure is adjusted to 1800-1850 PSI. I am confident it will end up being a 40 shot at 40 FPE when I am done.
