welcome to the world of pellet testing, only slightly cheaper than a pcp rifle in the first place, stick to the major brands and if you want to be really anal, weigh a batch of pellets, clean the barrel after every brand, pump through about 20 pellets before going for the group, fill to the same pressure before each test and to make sure YOU don`t come into it clamp your gun in a workmate (only works with pcp`s), been there, done that, still got 25k pellets that I wont use except for plinking, have fun