Depends how welll you can balance the reg and the hammer and what power level your trying to achieve , I played about with mine for ages , went with a little less power , averaged 11 FPE with Exacts 8.44 , managed to get no spike when it came off reg, but when it did it was a massive drop

Shot 153 768 fps
Shot 154 746 fps

Not a fluke , had several full cylinder string test while setting it up, all around 15 mags from a full cylider till it dropped of the reg , regardless of where the pressure guage was , some people shoot their's different and only ever follow their guage pressures, they shoot down to where green meets yellow , then stop, I do normally , but I know its got several more properly regulated shots in it If I needed them

HW100 S in .177 , quite happy at that power , I know I'm safe if I use Exact Heavies as they take the power up , I could re tweak it and get it slightly more consistant , but Its not bad as it is , normal Exacts don't seem to be the most consistant pellets anyway lately , I've been getting far better very low FPS spreads with Express pellets during testing just lately , Exact seem to be very hit and miss recently as well

Guess which pellets I have the most of