FX FX Panthera slow recharge rate.

This rifle takes a couple minutes to get back to the set pressure or even get close to the set pressure. I bought a Huma reg and it helped a little bit. Is there a screw too tight somewhere restricting air to the regulator I can check?
You might try degas your rifle.
Unscrew the regulator. Look at the little holes in the large brass section. I had a couple of them that had burrs from the machining process. After I cleaned them out with cutting torch tip cleaners it recovered much better.
Your head is fine!
 
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honestly I don't know. It may be there to facilitate machining.
 
I put the huma in my hunter compact and it works flawlessly. All I did was removed the factory fx regulator and installed the huma. No polishing or greasing, it works great. Even sitting 3-4 weeks, it may creep 2-3 bar that’s it. A very fast refill rate. Hopefully you get yours sorted out.