Bit of advise if you can, I decided to chrono my hw100 in .177 using jsb heavies in the garden, put a target out at 19yds to aim at and had the f1 chrony at the muzzle, I filled the hw to 200bar, now my first shot read 637.6 on the chrony and after 5 full mags (70) shots the highest reading I got was 736.6 and I was down to 105bar, now out of all 5 mags I never got a consistency most shots seem to go up in fps by a little bit, even tho the target at 19yds was just a large one hole group until I got 3/4 through the 4th mag then the pellet started to hit high, do you guys think it needs a servic