FX Impact M3 LOW fps

Hello
My impact m3 is .22 700mm sniper upgraded to superior barrel, power slug kit with tungsten hammer, I’m using 34g hp slugs in 217 but not able to shoot above 970fps with 1st reg at 180bar
And 2 reg at 150bar and my C1 is at 6.5mm
And macro at 15 and micro at 4, kindly help and explain why is it that I am not able to shoot above 1000fps, please help
Thanks in advance

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