Hello. Got my fx impact x .25 standard 600mm from airgun Depot. Been playing with it or a week now and I can't seem to get the jsb heavy to 880 or more. I read on forums people are getting over 880-930 fps on their impact. Are they talking about the impact with the old smooth twist barrel? Maybe the 700mm x barrel? Cause I'm using the 600mm x barrel and can not get no where close. My max with heavy was about 850fps. That is what valve on 4 lines, hammer on max, reg 150. I turn the screw left of the hammer dial so there is no play. I even crank the reg pass 150. Probably 160, and can't even get past 860. How do all these people saying they can easily get their impact to shoot past 880 when I'm struggling to get 860?