Are you saying the reg pressure fluctuates between shots? If so, it's possible it needs to settle in but more likely something wrong.
If you're saying it has a higher pressure right after a fill then drops off after a shot or two, I'd say that's normal.
When I fill mine, the reg pressure gauge always reads a few Bar high. What I do is burn two shots (no pellet) and then it's good for the rest of the fill.
I think it's normal for the reg to fluctuate a couple of Bar from fill to fill until it settles in, maybe around 500 - 1,000 pellets. Mine took about 1,000 at 140bar before the needle settled solidly on 140.
But even my worst ES was about 20, which is more than acceptable on any day. The fact that mine has produced single digit ES several times is just fantastic, and goes to show that tuning the hammer spring to the reg pressure is totally worth the time it takes to do it.
I didn't keep good enough notes but out of the box, it was 140. After filling the bottle it was 155, after shooting two magazines it was 150. This morning it was at 160 after sitting all night.
I decided to lower the regulator pressure to see if the pressure would stabilize, so I pulled the bottle, degassed it, screwed it in some, put the bottle on, and adjusted it to around 130.
My hearing isn't very good so I didn't notice it had a leak but did notice the bottle pressure dropping faster than normal. I put the rifle up to my ear and could hear the air coming out.
I pulled it apart including pulling the regulator, didn't see anything obvious, put it back together, no leak. At the moment I have no clue what was leaking but it started right after I pulled the bottle, degassed it, screwed the regulator screw in and pressured it up again. I did turn the adjuster screw out (CC) a couple of times to bring the pressure up, but that's all I did.
I didn't have any luck with adjusting the hammer spring at several different pressures, 140, 130, currently set at 125. The spread was always 40-50 between adjustments I couldn't really tell where the peak was.
I finally gave up for today, set the hammer spring housing clearance to 8.5 mm, shot 18 over the chronograph and ended up with an average of 903, ES 49 with the regulator at 125.
I shot a few pellets at the target to check the scope and it looks like the pellets are hitting the target sideways, it's making an oblong hole, not a nice clean round one.
Maybe tomorrow I will clean the barrel and try some non lubed pellets and see if that fixes that issue. It seems to group well even with all that's going on.
Cheers, PB