Snowpeak Artemis PP800R - How do I reduce to ~500 fps and tune for more shots?

I recently picked up an .177 Artemis PP800R, because it is supposed to be regulated versus the unregulated Diana Bandit.

When I shot it with Crosman 7.4gr pellets, I'm getting about 6-7 shots at around ~800 fps consistently, but then after that the pressure gauge hits yellow (100 bar) and then the FPS decreases linearly until about shot 21, when there isn't enough air to push the pellet out the barrel.

I already tried tuning the built in regulator setting by taking off the pressure gauge and turning the screw clockwise, but if I turn it too far down, the gun will stop working entirely (seems like the regulator valve will close off completely if screwed in too far). So the lowest FPS i'm able to tune it to is 750 PSI before it stops working. This leaves me around 8 shots at 750 fps, and 23-24 shots before running out of air.

My goal is fps ~450-500 fps, that way I can shoot indoors without it being too loud, and hopefully get a lot more than just 7-8 shots.

How do I further reduce the FPS? I'm thinking of cutting coils off the hammer spring, but how do I make sure I don't accidentally go too far? Are there replacement parts like a different regulator valve that will bring me closer to 500 fps? Or a tighter transfer port?

Thanks in advance, graph from my testing is below, gaps are from chronograph no-reads

2024-08-09 20_02_09.png
 
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Isn't that thread talking about the unregulated Diana Bandit / Snowpeak PP800 though? I have the PP800R, which is regulated (says so right on the box, and there's a regulator screw in the air cylinder)

The fps chart he's posted looks pretty unregulated since the fps shows the "bell" shape curve. Whereas mine shows a plateau, then a linear decrease.

2024-08-09 21_59_02.png


I'm 99% sure next step for me is to cut the coils on the hammer spring to reduce the weight, but I want to make sure I'm doing it right before doing irreversible change (If I had a replacement hammer spring I would have cut and tested already instead of asking for confirmation)

My PP800R also clocks in at 750-800 fps, while UK and Canada spec ones seem to clock in at ~500 fps. Does anyone know what makes those ones different? (transfer port size? different regulator? different hammer spring?)
 
Maybe a lead to look up nubnles stuff or contact