Some guns may need a good few pellets through before settling down, I would shoot 10 or 20 pellets through it then try it through a chrony, I have 3 x mk1 80s , 2 of them after the first pellet or 2 settles down with hardly any variance, The other one tends te shoot late 11s for the first 8/10 pellets before dropping around 11.2 Some will take 1 or 2 shots some may take a good few more , Regular shooting normally wears them in quicker,