HW90K 177 tuning help

I have a HW90k that I think might have an issue.

With the pressure pumped to around 18bar I get a large fps spread from 720 - 770 using JSB diablo exacts. I feel like 18bar is a bit high for the fps I'm getting in 177? The barrel has droop but looks completely straight so I'm assuming that is coming from the lockup; could that be enough to effect spread and velocity?

Thank you.